First off it's more complex than just straight randomness. There's a 'dice roll' every so often, like every half hour or so, to see if you get something. However those chances change depending on how long you've played that day. Something like after 2 hours your chances severely drop of finding anything. I can't give any real specifics, but I understand probability.
There's some other mechanics to it as well. Because with a system of pure randomness there will always be some people who never get anything and some people who get everything and I can only assume Valve would not want that for the items. I would suspect they'd incorporate a system that is cumulative, i.e. for every time you don't get an item, your chances of getting an item next roll are increased until you eventually get something.
However last they talked about the 'random' drops they admitted it to being broken. I suspect they're trying to really hammer out the bugs and test it out before rolling out an update with it. After all, when they first unrolled the new system, they had a bug where some people got every item in like 10 minutes, which I'm certain isn't what they wanted. The drops are Valve server side
anyway though, so if/when they do update it, we'll never know.
One last point, they're going to add more clothing items, at which I can only assume would increase your chance of finding any of the clothing items. That is why hats are so rare because they don't want everyone to have everything. Also they are going to roll out a trading system.
TL;DR:
A pie graph like that is meaningless with a complex system and a system of pure randomness wouldn't work.
I got the only hat I wanted: Fancy Fedora! I play mainly spy, so I'm happeh
I hate when people say stuff like that when some people have no hats.