It is a very nice pile of money to sit on. It gives Apple the freedom to be able to do something really big should there be a situation where it makes sense. For example, Apple was able to pay out more than $1bn for flash memory when it was a good idea to do that without worrying about the money. Dell would have had to go to the banks, Gateway couldn't have done it.
Granted, Gateway's only got about $400 million on hand, but Dell has over $5 billion in the bank - hardly a number that would have them going to the banks if they wanted to initiate a large purchase...