If you exclude the cash horde (edit - the zombies hired to protect the vault full of cash), Apple's P/E ratio is running at around 5 right now. IBM is 10. Microsoft is about 35 if excluding their much smaller cash pile.

Apple is ridiculously "undervalued" compared to any peer in the industry. It is a money printing colossus.

Having said that, the market seems to get shivers around $600B, and that psychological barrier imposes a friction that makes the rules of the game change. No one can stay above that for long, and in the case of Apple its profoundly out of scale numbers makes everyone simply put it in a different universe of valuation.