Actually there are games on steam they cannot take away from you. I myself have played the eve online demo with a full subscription, installed through steam, and even launched the steam installed version without steam installed. Your blanket conclusion is incomplete.
One thing you are however forgetting is what STEAM grants you beyond past methods of distribution, and that is infinite portability. I personally have gone over to my friends' house, logged into steam, installed a small game or even larger games at their place, without any coughs or issues. Why is this good? Because I installed without the disks, or even having to prove I was me beyond my account login. While this won't necessarily work for every game on STEAM, it works for a notable majority. This is simply one of the benefits STEAM offers you over conventional (store/mail) distribution.
Some other features which STEAM offers quite well is the community/group/achievment and other cloud systems. VALVe is trying to increase the titles which have cloud configurations enabled, with the intent of logging on other systems and having your personal configurations (ala config files for tf2) follow you around. Furthermore, you can participate in coordination with communities and groups in STEAM both with a STEAM client and through the steamcommunity.com website (with limited capacity).
The fact of the matter is STEAM is greater than a simple method of DRM. It is an improved method of distribution through portability. There are plenty of other benefits too such as granting developers a centralized forum to communicate directly with their fans, the ability to offer promotional offers such as gift passes, discounted weekends, centralized distribution of demos, and plenty more.
It is not fair to focus strictly on one element of STEAM without balancing it against the rest of what it has to offer.
I for one (heart) STEAM.