Mobile IE is upgradeable, independent of Windows Phone 7
One area that is crucial for Microsoft's success with Windows Phone 7 is in the browser. As the iPhone has demonstrated and Opera fans know, if you have a good browsing experience, you'll have a dedicated following.
Mobile IE has never really been great and while it's better on WP7 e.g. containing
...four-point multitouch fully enabled, zooming in and out by a pinching finger gesture on the screen, so-called "deep zoom" for extreme, high fidelity closeups, a remarkably clear typography, and very smooth, fast operation
...well, it doesn't inspire that much confidence. In fact, with greater enthusiasm for the desktop IE9, the mobile version (based on IE7, little bit of 8) seems like last-year's technology (and that's being generous).
Luckily, Microsoft may have a trick up their sleeves. It was revealed in the comments on the Mobile IE Team blog that the browser can be independently updated of the whole OS i.e.firmware.
Q:Will the browser in Windows 7 get more updates more frequently than only with full firmware updates?
Yes, we are building in the ability to update the browser independently of firmware.
While we knew OTA updates for the OS were a big deal, selectively upgrading just the browser can give Microsoft more flexibility in getting Mobile IE current. Of course that doesn't guarantee that those updates will give us a killer browser, but hey...options are good.