Apple now makes something like 60% of its revenue from products that didn't exist 5 years ago. I'm sure they realize this and will continue. When they stop they wont be center stage anymore and they probably know this.
Google has been trying almost everything there is to try. It's been almost exclusively failure but their pockets are deep enough that they'll probably get a hit eventually. I guess in that sense they are the closest to Microsoft's current position but they haven't built up nearly the same amount of bad blood yet.
Facebook I have much less faith in. Everyone I know who uses it only does so because they can't find a good alternative. That's a bad situation to be in if you're going for the long term
I don't know enough about Twitter to make a comment.
- Apple: May be in less than five years a cheap generic chinese mobile clone will have all the iPhone capabilities.
- Google: Search irrelevant, a lot of competition in the advertising arena.
- Facebook: P2P or other kind of social networking.
- Twitter: P2P too.