Even though the Dell Streak was always supposed to be offered in several capacities in the UK, up until very recently only the 16GB version has been available. It's still the only option at Dell UK and Carphone Warehouse, but O2 is now showing that the elusive 32GB Streak is in stock for "free to £249" depending on the monthly plan. The no-contract Pay & Go price is £449, £50 more than the P&G 16GB Streak.
Once Dell UK starts selling the 32GB version, there's probably a good chance that the Streak bound for the US will ship with the larger microSD card as well. What do you think, $499 (32GB) and $449 (16GB) unlocked, $249 and $199 with AT&T (and maybe T-Mobile) contract? That would be my guess.