I really don't care for the changes they made to the Tyrion/Sansa wedding in this episode (apart from obvious production realities ones), but I've gotten used to the writers being unwilling to have Tyrion do anything remotely unheroic.
It's been a while since I read the book, but with the exception of Sansa kneeling I can't think of any significant changes from the book. How was Tyrion unheroic in the books during the wedding?
1. Tyrion did not really object to marrying Sansa in the book. He was eager to be Lord of Winterfell, and hoped that he could make Sansa love him. Tywin did not order him to do it. He made an offer, and said that if Tyrion didn't want to he'd get somebody else.
2. On the wedding night, he had her strip naked and groped her before deciding not to go through with it (that part, obviously, was obviously never going to be filmed because of the actress' age, if nothing else).
3. Tyrion did not tell Sansa in advance in the books about the wedding. He allowed her to find out ten minutes before. The show changed that, as with all the other changes, to make Tyrion look sensitive and caring, and to play down Sansa's horror.