Not sure if this has been mentioned earlier in this thread, but noticed this today:
The offers for the US Mastercard via mail and email always have bonus miles up to 40K (30K and you need to do a balance transfer to get the additional 10K). For me anyway.
Today I actually noticed that the math for "your miles" and "your miles with a US card" didn't work out to 40K but 45K. Turns out the tiny link in the US website when logged in and looking at your miles balance, takes you to a 45K offer (35K with 10K for transfer). All the rest of the conditions and terms stayed the same. But this offer also specifies 2 miles for USAirways purchases, which the paper offers didn't. Maybe I just missed it in the fine print but I looked and couldn't find it.
So actually a better offer than being "pre-selected" or clicking on the generic card offer.