From a marketing perspective, the answer is obvious, tablets shouldnt expect to run any desktop apps, you'll need to buy new ones in the store.
But leaving out desktop apps is for the better.
This communicates with a desktop app to allow you to transfer files - very, very slowly.
In a lot of ways browser based applications are a step backward from desktop apps.
Playlists that I create on my mobile device appear on the desktop app.
The service can be accessed through the web, desktop apps or mobile devices.
The traditional desktop is accessible from a tile on the Start screen, or by launching a desktop app.
Compared to any desktop app (including Apple's Mail) it comes up desperately wanting.
That's most of what keeps me on desktop apps.
And being able to run real desktop apps would be very nice as well.