I have bought games from both ImpulseDriven and Direct2Drive before, and THEY don't have any intrusive programs which you need to install and run everytime I want to play my games.
I'm too tired to anolyze D2D but both games I bought from them (never again!) had slightly different structures: mods wouldn't work with THIEF3 and DEUS EX2. There was no easy way to fix this so the modders did not waste time doing so - and neither should they have to.
There are other not-so obvious issues because the .exe files for D2D are "cooked" - the Fallout Script Extender for example is incompatible (it is compatible with up to date Steam versions). More on that http://geck.gamesas.com/index.php/Fallout_Script_Extender
