Speaking about this, the PS2 is now beginning to get emulated on the PS4.
Thing is, Sony wants you to a pay money just to stream Achievement-Tweaked chunks of game, rather than be a cool dude and let you play your old PS2 disc on the PS4.
Say what you will about Wii-U, but you can pop in your Wii disc you bought, and play it on your Wii-U with no issues.
The PS4 wants you to pay to stream-download (Not own) games for a price, only to get some little picture trophy that's triggered when some memory address on the emulation is altered (100 enemies on Dark Cloud - here's a crappy achievement).
Nintendo did BC from the beginning this generation and they're great for that. MS is trying to play catch up and Sony is trying to use MS's attention from it to drain more money from the consumers.
It's like BC on the PS3 slim models: hey, boy, put ur PS1 discs in, but NOT your PS2 games... Those u have to pay for. And then fanboys are saying "They can't read the disc in the PS4"......... I guess the PS4 can't read DVDs then, as these fanboys are watching a DVD of polygon man commercials.
Sony has no excuse. They can easily let people use their PS2 discs in the console, but there's no money milking in that. Ms is letting u use discs, which is FUCKING great, but they can't do all titles at once, and most titles they won't even bother with, which sucks but at least no rebuying. Nintendo wins, tho, by having 100% BC from the start using discs.