AS soon as they added the internet to consoles basically everything you want in a consumer device was possible. Almost nothing being done on the PS4 can't also be done on the PS3, a bit of software to share pictures and crap, a bit of save game stuff and wireless connection to a Vita to continue a game on a different device, this is basic basic stuff, cross game chat, again even the PS3 was basically a PC with more than enough power to program this kind of crap into.
The ultimate difference is more power, more efficiency which will lead to better graphics. People can pretend all they want but graphics were the very obvious main driving force between consoles and always has been. If you could buy a PS3 today or a Saturn with vastly inferior graphics but all the same other functions who would buy the Saturn, same for any console comparison. In 5 years people will look back at a 360/ps3 and think the games look old and dull, thats life.
its a new console with better graphics and everything else is minimal software differences that could almost all be VERY easily implemented on other devices.
New controller... I'd love for someone to explain how its impossible to add a new controller for the PS3.
I find it funny that some people think a hardware upgrade is no good reason to upgrade one device but its the only reason people upgrade other devices. There is VERY little you can't do on an early iphone or any early smart phone that you can't do on a later one, just more power available, prettier graphics, faster content switching, its still the same stuff, office aps, basic games, phone calls, video watching, cameras. People buy new ones all the time because its faster and has more power than the old one and for no other reason.