So because of DRM, they're fully capable of taking those games "back" (removing them from accounts), right? I mean, if VALVe one day decided I no longer can have TF2 they can simply strip it from account, is that how their terms work?
It's a blanket policy and a reason why I never use Paypal for Steam, use a real or "throw-away" credit card for Steam purchases. Alternatively, you could not buy from Steam at all, I don't anymore but it's too late for me. I already have over 200 games with them and worry about losing access to everything.
I've also heard that Valve will remove games that were acquired through the trade system if the original buyer obtained them fraudulently.