One guess: If Congress thinks GoDaddy is the sort of company that will help them manage all this unruly internet stuff, then that's the sort of company Congress wants around.
Congressmen live and die by response to constituent concerns. If the folks get worked up about cyber-bullying or unsafe skateboard videos or kitten porn or whatever depredations those Internet freaks invent next, Congressmen want some avenue to Do Something. GoDaddy may get little from SOPA, but they could get a lot offering to help manage all of this . . .