Apparently it's Microsoft's fault. Quelle surprise? I can't say I've noticed this problem being too bad myself but there seems to be plenty of Steam users annoyed, in your typical Internet fashion, by repeated installations of the latest version of DirectX.
In a post replying to these complaints, Valve admin JMcCaskey claims the problem lies with DirectX's helper library, called D3DX; there can be up to 40 different versions of this file which are tied to the actual compiler for the game.
"Even if a later version of the binary is already installed, that version cannot be used, and even if your DirectX install is up-to-date because you've run a more recent version of the installer that is not guaranteed to have installed all previous versions," said McCaskey. "We can't stop, it's required due to a bad versioning/packaging scheme as well as bad redistribution licensing terms on the D3DX libraries."
As someone who tries to keep their PC clear of clutter and unwanted programs, I can understand people getting annoyed by seemingly having to re-install the same piece of software over and over again. In fact I can remember that PC gamers were encouraged to uninstall previous versions of DirectX in order to insure against potential problems. That being said, I can't remember DirectX ever stopping me from installing or playing a game on my PC. What about you, Destructoid readers: repeated DirectX installs a problem?