4.) The PS3 is the only way you can play PS1 and PS2 classics for now.
If you grew up with the first two generations of PlayStation consoles, you might have a lot of PS1 and PS2 classics in your digital library. I still play Final Fantasy VIII, Crash Bandicoot, and Syphon Filter 2 on my PS3. I know that a lot of other players might not have access to their old consoles anymore, so the PS3 acts as their gateway to a trip down memory lane using one platform.
Unfortunately, next-generation consoles like the PS4 won't have backwards compatibility and our classic titles won't instantly carry over to our new consoles. The good news is Sony is definitely working on making most, if not all, of their games from PS1 to PS3 available on the PS4 through Gaikiai.
The bad news is it might take a while for all of their past games to be readily available to players. If I'm not mistaken, it's also unclear if you have to buy all these titles once more. For now, here's a report that suggests that we won't need to expect the worst.