When your looking at a huge change like the HD-GUI, yeah you need to do it in small groups to not overwhelm the call center. Sure it works great, testing has proven that. However there are MANY people out there that cringe at change. The moment they pull up the guide and things look "different", they are going to think what the heck happened? They might call in and ask... flooding the call center. There are people who will be opposed to certain features, things that confuse them, etc...
Anytime you change the entire look of the UI, you need to be careful about rolling it out.
If you want it sooner and would like to contribute to testing new releases, feel free to check out the CE program. That is what it's there for. No other provider has such a unique way of testing software updates. You won't find that with Cable, fios, uverse or dish. Take advantage of the great CE program to test drive new releases. Just check the CE forums to see if they are on schedule for the usual Friday and Saturday nights.