I can play Angry Birds elsewhere. I don't need a phone to play it.
I also strongly disagree that 3D is the main selling point of the 3DS. The main selling point, for all gaming systems, is games. Always has been, always will be.
I feel like that's something gamers are telling themselves to make themselves feel relevant. If games were what mattered the Kinect wouldn't have been the thing to make the Xbox sell like it's an Apple product and the PS3 wouldn't be eating dust right now. Games are important, don't get me wrong, it's just that they many times come second to other things (Like the wiimote, 3D or the Kinect). As I said, I believe the 3DS without the 3D would preform just like Vita. In essence: Without something to set your product apart, you won't move it, and if you do in theory but you don't have the software to show it, you won't sell it either. You need both. That's the way the market is right now.
Angry Birds right now is considered by many as a game for their smartphones. That's where they play it, that's where it sold the most. But that's no the point - there are a million games for smartphones and most of them cost like 1.99$. Sure, they are no match in production value, but that'll change. The more profitable these games become (and they're becoming very), the more funds people will direct their way, the better games they make with better production values, and eventually hits emerge and IPs will get established. And because, as I said, games do matter (just not as much as some people think), the phones will become a viable gaming platform. Death cycle for handhelds will commence (less users, less reasons to support it, less software, less reasons to buy it, less users.)
Right now there isn't that much more, not of that magnitude anyway, but I'm showing killer IP can rise in mobile games, and Angry Bird's rise was meteoric, and more will come eventually. It's a matter of focus and funds. The couple of people who are discussing making a game in their basement right now? They're talking about making it for the iPhone or iPad - That's where the people are and that's where the money is.
To be clear - that's not happening to day or tomorrow, but in 2-3 years.