First off, I'd like to say I've converted 2 3.5 True Believers (No! There is no other ruleset than 3.5! They like the number 3 so they started it there! No such thing as AD&D! LALALA!), one who looked at the rulebooks and stormed off, and another who played a beta game and hated it.
Which goes with what I say: Actually play a real campaign with a real DM, not a demo, and you'll find you like it.
... explained the non-relation between character optimization and player role-playing. People would get into arguments "Oh, excuse me for not min-maxing my character, I like role-playing." as if someone who put a lot of work in making a good character must also be incapable of role-playing. ... I'm seeing the same relation in how you're looking at the rulesets.
Interesting. No I hadn't heard of that, and I'll look it up sometime after I post. But based on your summary... no, that's not what I"m intending to say at all.
I have a friend who is a 3.5 Rules Lawyer. The whole "dual wielding vorpal blah blah blah I have to roll critical fail to lose" deal. The ultimate in 10 sourcebook minmax. And he's one of the best roleplayers I know. So I'm not saying that either system enhances, or degrades, a roleplayer's skill.
I'm comparing the rules style to a style of roleplaying. 3.5 is very detailed in it's rules. You look at your character sheet and notice that you have a -7 to save on Poisons which are Necrotic and also Blue. Therefore you frame your character in such a way that blue liquids near cemetaries cause him to run in fear. This is "method acting," and there's nothing wrong with it. What's my motivation? I insta-die when I look at blue necrotic poisons. Completely valid, and can be roleplayed well. My Evil Cleric in the 3.5 campaign can't spontaneously cast
cure spells, and my DM offered to waive that rule. I said no; I'm going to play Quaternion within the bounds of the 3.5 ruleset, and let that shape the way I play him.
Compare with 4.0 Saves are always 10+ to save. Powers have set abilities. Saves are set like AC. There's not a lot of nitpicking in the rules. This allows a player to improv his character more. If he WANTS to be afraid of blue necrotic poisons, because he thinks it would be fun to play, he can.
In 3.5, you can play against type. The Rules Attorney above once played a rogue with a Fort Save of almost nothing... but also with a low Will Save and a low Wisdom score. He decided this meant that he was deathly allergic to EVERYTHING, but also that he had no impulse control and also failed to recognize that quaffing every glowing bottle of goo was a bad idea. And that's how he played it, and it was awesome.
Each system is completely valid. You can be as free as you want roleplaying in any system. I just feel that 4e allows you to buckle swash easier than 3e. Rules Laywer above would have an easier time quaffing glowing potions if he knew his Fort Save was 17, instead of "roll and maybe you save if you get a nat 20". But on the other hand, would he have ever thought of that "drawback" without the numbers? Experience says no!
Rules Lawyer is a method actor. He wants his numbers to play his character. Valid, and awesome. He wouldn't much like 4e because of the looseness of the rules. And that's fine as well.
The way the 4E rules are set up is meant to allow new players to pick up the rules quicker while also allowing DMs to put out well-thought adventures and balanced, interesting encounters with less work. That being said, I feel that regardless of which system you're using from First to 4E, players and DMs are capable of roleplaying however they want to. The rules only form the skeleton for creating a fun game structure focusing on combat. Outside of the battle, there is little to no use for almost the entire PHB.
I agree with the middle. If you knew how many arguments we had over the rules (with one player being completely new and not contaminated with that 3.5 swill (flamebait!

) you'd know that that line about 4e being simplified is hogwash. The arguments just change. Arguments in 3.5e is about some esoteric line at the bottom of a footnote on an errata page for a book only 6 guys bought. Arguments in 4e generally lie around if said rule is actually applicable to the situation. Sure, I could heavy-handedly invoke Rule 0 ("The DM is always right and if you don't like it rocks fall and kill you and everyone you love."), but I believe that solid rules let players know exactly what an action will entail (rules wise).
Plenty of arguments all around. However, as a DM, I will agree that setting up the adventure is so, so, so much easier. I count the players, figure an XP budget, then buy monsters. Add traps. Done. In an hour I've got 8 encounters set for the next mission. Roll some treasure, and the entire rest of my copious free time is set asside for set dressing. I love it. Also, adjudicating actions in battle is much easier for me, the DM. With simplified rules and rolls, I know exactly what to call for 90% of situations.
As for the final stab at the PHB, we actually end up pulling out our 4e PHBs quite often outside of battle, but mainly because my players keep pulling out awesome abuses of the rules during play (Note: I reward awesome abuses of rules.) My experience with 3.5e shows me that newbies either get themselves killed trying stupid things all the time, or they just hang back and fear doing ANYTHING for not knowing the chain of deductive reasoning through the rules that they see the lawyers around them pulling, finding out that vaulting the table is a Strength, Jump, and Tumble check, or whatever. In 4e, I have said swashbucker roll an Acrobatics and then make him explain himself when he fails. In this case simplicity DOES matter, but that doesn't stop players from trying to convince me that their whirling sword would give them lift or something and trying to bluff a featherfall.
But that's the joy of being a DM. Nothing like saying "Sure, I'll allow it" and not saying the "with a DC of 40" part.