Should all gamers require Steam activation at one point, Valve could ask for whatever fee they want from publishers who then have little choice. That's an absolute extreme, and I don't think that will happen. But should a company have too much power, that's possible.
Are you saying that Steam can take all existing Steamworks games, and suddenly go "SURPRISE BITCHES" and demand a fee from everyone who's ever used it?
Because if that's your concern, and if for some reason Valve did suddenly decide to become shitbags, legally, that can't happen.
It's called
Estoppel. Almost certainly
Laches as well.
Read above, nobody can guarantee that Steamworks will be free forever. Again, should gamers require Steamworks integration, Valve could become quite powerful.
And should it become expensive, how do you know those people will leave that platform? That does not work together with people saying "No Steam, no sale" as these guys apparently do not care all that much about pricing. Otherwise they'd buy games on Amazon.com when they are cheaper on there already.
I don't know the story about GFWL though, just have a few games for that and that DRM is a thousand times worse (but at least I'm not forced to use a client).
If you're saying at some point in the future, future versions of steamworks and future games using them might require a fee;
so what?
The middleware Steamworks currently replaces require a fee.
Some publishers are already 'double dipping' by using Steamworks and additional middleware that provides the same functionality.
As long as Steamworks has tangible benefits to a consumer (it does) and customers prefer it (they do) it is beneficial for publishers to use it.
If Steamworks becomes distasteful to a consumer (as GFWL is) and they avoid products that use it, the market will see it used less often.
It really doesn't matter how many other titles use a middleware if something better comes along; when's the last time you used a Gamespy ID to play multiplayer? A metric fuckton of PC titles used Gamespy for their online prior to Steamworks.
EDIT:
To address your specific points about GFWL and amazon;
1) People
like steamworks; this is why people ask for it, and are happy to pay a higher price for titles that use it.
Or indeed be extra happy when they can buy a title on amazon cheaper than on Steam, but then use that cdkey on steam and gain all of the benefits Steamworks provides.
2) GFWL when it launched required an XBL Gold subscription to play online.
You might not know this. Because it was dropped slightly slower than the sales of any games that used it plummeted. Because nobody is prepared to pay money for p2p gaming on PC.
