FWIW, Apple and Google are both overvalued. :)
Well as you said: 'growth bets'.
Google are a long bet, I reckon. So far they're proven for putting out good products. But to be worth the money they need to monetise at least some of these.
Up to now we have one success in that department: Adwords, which is extremely well thought out. But it's still just one point. They may not get another multi-$b cow.
Adwords even if they manage to fix content ads, would be pressed to find that much growth (but 100%-200% is not out of the question)
Apple may be justified. There is the old mantra of 'be very good at 2 things' instead of 'be the best at 1 thing.' Apple can do:
1- Software
2- Hardware
3- Marketing / Product Launches
4- Creating Markets & doing deals that put a nice chunk of it in their pockets (Itunes, App store)
Take any 2 and you have a potential player in a lot of markets theat may grow very big.
- TVish markets (some future apple TV?)
- bookish markets (Kindle?)
- thin clients (If the free with internet accesss PCs happen, who better then apple to make them? Nokia?)
- gaming (could happen?)
- GPSish markets (you never know where this might go)
- In-Vehicle stuff (Ipod type thing for music & aircon & stuff in your new BMW?)
You almost expect apple to grab a piece of any consumer electronics that come up. Problem is they seem to be running on momentum. Not sure that'll last forever.