From the same Comics Alliance post that announced that the Ultimate line was also going to include download codes in its print editions, here’s Marvel’s VP of sales David Gabriel:
If the digital comics going same day as print had taken off like this monster sales horse and destroyed the in-store comic shop sales of those print books… they wouldn’t have sold out each time we did another one. The retailers wouldn’t have been looking across the board for second prints on those books. Reorders wouldn’t have been coming in on the books. I think people thought at the beginning that everyone was just gonna turn to digital to get the book and not go up to a retail shop, and we watched that not be the case time and time again.