To call PC gaming a 'niche' market is silly. Especially Considering that steam alone has as many ACTIVE users as xbox live has registered members! If PC gaming is a niche, so are consoles (even moreso in fact, the low estimates are that there are 150m PC gamers, compared to the ~60m current gen console games on 360 and ps3 combined).
The fact is that EVERY developer that has the ability (game, engine and knowledge wise), first party restrictions factored in, to make a cross platform game will, because it earns them MORE money! Why would anyone NOT release an FPS game, a genre that is popular on consoles too nowadays, if their engine can do it? Crytek didn't have the ability to do so with their cryengine 2 engine as much of the rendering tech was still too cumbersome and processor heavy, but over the 5 years effects such as HBAO have become much less taxing. Therefore with cryengine 3 they thought 'we can manage this now' so they did!
It's not that PC gaming is niche at all, it's because PC doesn't have anyone forcing a developer to only develop for that platform. if i were crytek i would've made crysis 2 multiplat too. I just would've handled marketing better with a PC focused edge (ala DICE) because every digital PC game sold (and over half are) is the equivalent of 3 console games sold at retail profit wise.
Anyways, the only reason PC gaming doesn't APPEAR to earn as much money compared to consoles is because digital sales aren't factored into that. Now, we know steam alone took in over $1 billion on it's own last year, so deduce what you will from that. If you can't deduce: factoring in steam and world of warcraft (and nothing else) to retail PC sales, PC is the top dog by a long way. Factor in casual games? Yep, you've got the platform which makes up over 50% of the revenue of all gaming in the western world (in the east, PC just thrashes everything because of china and their obsession with PC gaming).
The ONLY reason PC gaming APPEARS to not be as big as consoles is because a PC is not a fixed product like an xbox. The estimates of numbers have to go off how many gaming class gpu's are sold by amd and nvidia (normally assuming 1/2 are used for gaming for the low estimate), and that's not the kind of information places like IGN are interested in. With the xbox? they can just say x were sold in x month.
PC is not as controlled, therefore it's harder to pin down stats about it

But don't worry, the companies who're in charge know how much PC makes (EA recently said the PC will become their main platform over the next year or two).