Let us assume that you are right and calling the name of the respective country gives the players a boost.
What do you care?
You are not such a player, the fans are not such a player. I would presume, that the players have brains, so if they are so unhappy they will address the "issue".
I care because as a fan and spectator, the Davis Cup feels special to me. I know it does to the players as well because I've heard more than one player say that when the umpire calls their nation's name, such as -
"Game, United States" or
"Advantage, Serbia" - it gives the players goose bumps and makes the match so much more special because they are reminded constantly that they are playing for their country and not just for themselves, like they do every other week of the year.
By not calling the nations' names and calling the players' names instead, the Olympics don't feel special to me, as it should. By the umpire calling -
"Game, Isner" or
"Advantage, Tipsarevic", the players are instead constantly reminded that they are just playing for themselves as usual. It's more like any other tournament on the calendar. And that's a shame.