Why is this considered a feature? two pc games not being able to play together is ... something everyone thinks they should be great full for?
wow have gamer really gotten so abused that this is considered a feature... "New feature this game has a 50% chance to NOT crash on start up! buy it now!"
I do wonder if your question was genuine or just sarcastic.
As much as I understand what you say, from a developer viewpoint is a different matter. It's not common to see crossplay between different clients (heck, even when playing lan through third party softwares you NEED to use the same tool with your friends, you can't simply use different ones and think that lan will work). Also, there are already games which do not have the crossplay features (see dragon's dogma, were we can't share pawn with steam users, and similar) so the concern people have is pretty genuine and justified.
I agree that PC gamers are abused, but I only agree when it coems to big pubblishers, not some indie devs, who even cared to put their game here and add crossplay with steam.