The biggest problem of PCs is the fast evolution of hardware. When you buy a game for PS3, you know it will work well on your PS3. And when you buy a PS3, you know you'll keep finding games for it, even in 3 years from now. And I bet there are still titles released for PS2. That's the only advantage of console gaming and is quite a big one.
The fast evolution of mobile devices is actually a disadvantage for the kind of people that buy gaming consoles in the first place.
However, console gaming has been a niche for quite some time. This is not new. The exception was Nintendo's Wii, but that was just a fluke.