Lack of money hardly has anything to do with Andy + Kim tying the knot. She's not poor either. In Andy autobiography he says his parents divorce makes him aware of how important it is to have a lasting relationship.
Therefore he doest seem to be the type to take relationships lightly, like some rich and famous people do.
They live together, so there's no urgency.
Suppose but his brother married very quickly and romantically. One of the many things I dislike about Federer is that he only married his girlfriend of ten years when she was having a baby. I think Andy will be lucky if a lovely girl like Kim is willing to hang about for years without commitment from him. If he loves her he should want to marry her - old fashioned I know but still true.