I can think of only one reason why you could buy a branded phone: because it's cheaper then the debranded version. So your phone will be full of the carrier's crap and that's it. If Sony-Ericsson would remove the crap then the carrier's intention of customizing the phone for you (whether you like it or not - and you are supposed to like it because you knew this when you bought the phone) would be useless.

Also, Sony-Ericsson has agreements ($$) with the carriers for branded content.

So you bought a branded phone outright and you knew this and Sony-Ericsson has no reason to debrand it for you.