One issue Sony had with the Playstation 3 is that it wasn't fully backwards compatible. There were a few console models that allowed gamers to play PS2 games on their PS3, but Sony stopped producing those models early on leaving PS2 owners in the dust.
With the Playstation 4, Sony is looking to fix all of that. Sony announced the "Playstation Cloud", a service that will stream PS1, PS2, and PS3 games to the system. This solves the backwards compatibility problem, and also explains why Sony bought Gaikai last year.
David Perry, Gaikai founder, talked about Playstation's willingness to use this streaming service for "everything ever", but no games were specifically mentioned. Perry also said the Playstation 4 won't play "Legacy" discs, making the cloud service even more useful.
The "PlayStation Cloud" service will be rolled out gradually over time, most likely meaning early adopters won't get their hands on the functionality right away. Besides, it's not like consoles always work like they should right out of the launch gate, right?
Sony's Playstation 4 is set to launch holiday 2013.