Angry Birds has been popular for what? 4 years now?
There are plenty of fads in the console game business too -- Wii Fit, Wii Sports, Just Dance, Guitar Hero, etc.
Mobile gaming as much as some people hate is not going anywhere. If anything more and more kids are getting introduced to their first gaming app every day. Cell phones are not going anywhere and there will always be games on them from now.
A smartphone is simply put the most important electronic in most people's day to day lives.
Nintendo fans are hypocrites on this, five years ago they were chiding Sony/MS fans for saying Wii Sports/Wii Fit weren't real games, now that Nintendo isn't the hot blue ocean brand anymore, they're using the same arguements against iOS/Android gamers.