Because MS doesn't have a competing product yet. Microsoft's business plan will ultimately concur the tablet market because they'll have Dell, HP, Sony, Samsung, Motorola, and every hardware manufacturer marketing and selling hardware with Mango pre-installed on it.
I'm not saying MS will necessarily have a better product, but fierce marketing by the giants will ultimately set a standard.
Same with what's happening with the Android platform, over time Android will outnumber iOS not because it's better, but because when you go to a store you'll be bombarded with Android phones that the iPhone will be a second thought.
It's exactly what happened with the Mac since its launch in the mid 80's
As for Apple making more money than Microsoft, um, no. Apple is the largest tech company according to market cap; however, Microsoft makes a butt load more money than Apple - NPR Article -