Actually, it would be quite easy to implement - when making roster moves it would return an error if any player you try to send down has too high a PB value.

But your point is valid, it would change the way the game is played. If you wanted to rest Bonds against a weaker opponent, you'd have to leave him on the bench (and tie up a roster spot) and give him a couple pinch hits to ensure he doesn't get rusty. And you'd have to do that during home series, which I guess would give you less enjoyment of playing Bonds at home. :)

It would make things a bit more realistic (yeah, yeah, this isn't real baseball). I mean, the idea sending a player with Bonds' abilities to the minors is kind of silly.