Well also remember DELL et al have to clear their channel of the 'OLD priced' T7700s, so it may take a few weeks. Some companies do more real-time pricing, but that sometimes causes problems for old users too, so channel pricing helps delay the transition. But really as long as people are willing to pay DELL the premium, they're likely going to charge it, once they see the option dip in popularity, probably then they'll change pricing.
Personally I'd prefer, like you, that they update within a few days of new pricing, but the reality is that it usually takes a few weeks for the prices to come down. And hey, they know they can squeeze more out of the T7700 & 7800 buyer. I've found the T7500 is the sweet spot usually right now, but with the prices drops that may change in a fw weeks.