They have a few competing markets, but they aren't the core business of Microsoft, meaning that they are not direct competitors. I actually don't know why Microsoft decided to make a Zune device which is the only competitor to Apple that they have done hardware+software wise.
The list was pretty bad except for Zune-iPod considering, as I said, Microsoft sells software and Apple sells bundles of software+hardware.
I'll agree with you on that. In terms of Microsoft's business, Zune and even Windows Mobile are small fry - attempts to coin in on the latest fashion. Big mistakes, they wasted money they needn't have, and that was probably when the comparisons to Apple started kicking up, because they put themselves out there and failed. (they're doing it still with Windows Phone 7)
Microsoft's core market is it's enterprise business - and that's great because Apple aren't actively interested in it.
However Microsoft aren't pushing the envelope. We get new versions of Office, but they're not that much different to the versions before -- in some ways they're actually worse. Ballmer doesn't understand how innovation works - he waits until a technology or market is already out there and being used (Azure anyone?), and tries to clamber onto the bandwagon.
The Microsoft of old, under Bill Gates, would have been buying up all these small developers - and they weren't afraid to upset a lot of people doing it. Ballmer wants to be big and cuddly, everybody's friend. Cuddly Microsoft is standing in the shadow of empirical Apple, and Apple are very sneakily getting their goods into the pockets of executives everywhere.
Apple may not want to (openly) go to the business sector, but the business sector may unwittingly come to Apple. Mountains and prophets.
The unavoidable fact is that Apple have all the headlines, they're winning hearts, minds, sofa time and very slowly bits of office time too.
Microsoft have all the resources to be able to grab the spotlight again - and the spotlight is incredibly valuable. They just need a new leader, someone with vision, leadership skills and charisma, to take them there. Until they get that, Apple will be seen to be winning, regardless if you or I think they're in competition.