Just my thoughts on this topic . . .
I think, given another 10 years (plus or minus), we're going to see systems overall become so similar in their capabilities . . .
Look at it like this; the most modern consoles are really just mini-ATX LAN boxes. There's a small form-specific motherboard with onboard CPU, memory, video and sound, a DVD-ROM is attached, and in most cases, there's external storage (HDD), LAN or other network connectivity, and I/O ports.
That, my good friends, is a computer at it's most basic form, and has always been that way, whether we're looking at a current xBox360, or an ancient NES or Atari.
Thing is, as console gamers demand more and more from their systems, consoles have been forced to start taking on more duties that were typically thought of as "PC-only" - high-quality, multi-channel audio; better graphics; internet connection; HDD storage for games, software, media, etc. Even recently, consoles have allowed for games to be downloaded straight to the console's HDD . . .
So . . . at our current rate of "console-modernisation," we can expect to see consoles continue to inch ever closer to a gaming rig. Granted, they'll never be able to overtake a dedicated gaming rig when you look at sheer processing power, but that's another story. As it is, you can guarandamntee that as consoles continue down this path, they'll start encountering the same "issues" that "plague" the PC gaming market . . . most notably, piracy. The first major "milestone" for this is a simple internet connection, and the ability to transfer media from one rig to another . . . and that capability already exists . . . where there's a will, there's a way . . .
The only major "kink" of developing for PCs is the vast differences in user hardware. Consoles have streamlined this problem . . . everyone that owns a PS3 has the exact same hardware configuration. Everyone that owns a 360 has the exact same hardware configuration . . . makes development a lot easier.
All I'm saying is that as we hike down the road - we're going to start seeing consoles start having similar issues to the PC as they become more similar to the PC.
And then what platform are devs going to develop for?
-EDIT-
Regarding kreij's post above, I tend to agree . . . as everything becomes more similar, why differentiate?