From the point of view of a third-party Windows developer evaluating Windows RT, I would be seriously insulted by Microsoft's behavior.
"Microsoft," I might say, "You're demanding that I not only rewrite my software to a new API, speaking a completely new design language, but also subject myself to your monopolistic sales channel in order to sell my software to your users?"
And yet Microsoft is not bound by either of these restrictions itself. It's able to keep its legacy software around, and it's able to leverage a privileged distribution channel: bundling with the device.
That bundled software isn't free, by the way. If you're a business, or want to use the bundled Office software for "revenue-generating activities," you must buy a license covering its use.