Well, I'd hardly expect Santorum or Christie to be cheerleaders for Team Romney. They have their own careers and aspirations. Both discussed issues important to the Republican party, issues Romney supports, and endorsed Romney at the end of their speech. To me, it would have come off as extremely phoney if both spent 10-15 minutes recapping how great Romney is.
As for Ann Romney(I didn't see her portion), she's not a public speaker. She raised 5 children(probably with 10 nannies) and rides horses. If one expects her to be Michelle Obama or Hillary Clinton, I think you're expecting too much. Both of those women want/like the spotlight. We don't know that to be true of AR. In fact, it's been said before that every time she opens her mouth, she hurts his campaign.