Here is Vashy's schedule for the next little while, per Stephanie Myles:
He’ll take a week off in Montreal, then start training again for the grass-court event in Newport, R.I., (where he hopes to play doubles with Lukas Lacko of Slovakia), then the Granby Challenger on hard court, then back over to London — and Wimbledon — for the Olympic event.
I saw one of the reason to pick Vasek was getting him a better chance to get into the singles since he would be there anyway.
I would think that if they had picked Milos for doubles then Vasek wouldn't have gotten the WC.
Also Vasek will more than likely lose in round 1 in singles, maybe round 2. So he will be more focussed on doubles. Milos could in theory medal in singles if all goes perfectly, so he will be focussed on singles more than Vasek