Re: Why Pakistani dude and white girls/women end up in divorce ?
Maybe their out-laws moved in, (just kidding - mine have been here since February, so my patience is wearing a little thin).
I'm not sure how many couples you know, so I can't make any generalizations about what went wrong. Many couples do grow apart when the kids leave home. Oftentimes they were never close to begin with, and the only thing holding the relationship together was the children. It is very important that children realize that the husband/wife relationship is the central relationship in the family, and the glue that holds the family together, but I'll save that for another thread.
I would guess that if you investigated further, you would find that these couples split for the same reasons some of your desi friends have divorced - money, loss of trust, lack of interest in continuing the relationship, and so on. Culture probably has very little to do with it.