Google is the only company you listed that has failed at expanding it's revenue streams - too early to say for Facebook and Twitter, and Apple is killing it at new markets.

Your post brings up the real issue: if you sit still you're going to die.

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.