Much of the commentary I’ve seen for today’s announcement of Windows Phone 7 revolves around whether Microsoft can catch up with Apple’s iPhone and Google’s Android. Fair enough; feature-wise, they are in the same ballpark.

But Microsoft need not triumph over the “big two” in terms of mindshare. In fact, Apple and Google aren’t the big two at all. Who is? Nokia and RIM.

Between them, their operating systems command around 60% of the mobile market — but this number falling rapidly. This fall is due to the uptake of app-driven smartphones. In other words, it’s raining customers for this segment of the market.

Microsoft isn’t really targeting Apple and Google, dollar-wise. They are looking at all the new customers coming in to the smartphone market. If they manage to get, say, 20% of the switchers, that’s millions of people.

Anecdotally, I am told of a prediction that RIM’s market share will halve in the next few years — while selling twice and many phones. Get it?

Microsoft is going after those former RIM (and Nokia) customers. There will be a lot of them.

There’s the old story of the two campers who see a bear charging toward their camp. One camper sits down to put on his running shoes. The other asks if he’s crazy. He says no: I don’t need to outrun the bear. I just need to outrun you.