I see it as a grey area, go back 3-5 years ago and many companies would scoff at the idea of creating exclusive PC content. It was a platform with rampant piracy and people would share their software repeatedly. With the recent years, Steam and a bunch of other services are giving more developers incentive to developers on the PC without risking money from piracy while other stills have their heads in the past.
It's also a market that's hard to enter, Blizzard controls 62% of the MMO Market and who knows how much of the RTS Market. We demand better graphics, cheaper DLC, Editing tools/Mods at a slightly lower price point. Sure more developers might enter the fray, but for now most will only play around with the idea.