Hmm, weird... haven't had any performance issues on my side, but if it isn't represented by your service providers, then that can be a problem. Maybe you know how many people in your country COULD have the same problem? I mean, does this problem impact the gaming market a whole lot or are those numbers I shouldn't worry about?
And, speaking about the internet connection you need to have to play a game downloaded using Steam, that is not a problem personally for me, seeing as my original idea is distributing the games using the internet either way.
Also, why I will be definitely using Steamworks - the problems you mentioned might cause a drop in the number of my potential clients, but compared to one of my games that don't use any of the possibilities Steamworks offers, that number will still be significantly higher!