The most telling sign of Steam being actually approached as a service (apart from me actually defending it) is probably its success on the russian market. In Russia you can get every piece of software cracked and free of charge of the internet. For a very long time piracy was the only way to get most software in Russia, heck, last time I checked you could actually buy pirated software in the supermarket.
Everybody told Steam it would be a disaster to move on the russian market. Guess what, they are making a killing over there.
Steam is, imo, only the most visible form of the shift from retail to digital. This shift was what actually put the PC gaming back on the map. Selling a game and getting 95% back as profits is something that you simply can't dream of in retail. That lead to massive discounts, which again drove users up. Steam is only the most successfull (and first, iirc) of the digital distribution services. So I wouldn't say that Steam single handedly revitalized PC gaming, but it sure is the most visible of the digital services out there.
The DRM part of Steam is less interesting to the average user as it was ten years ago, because internet is literally everywhere nowadays. That is, among other things, the reason I stopped my opposition to Steam. Even when I was in some godforsaken Hell hole of a country like Georgia, I still was able to play my Steam games. So any problems I could have with Steam were of a dogmatic nature, and games are not that important for me. (And as a strong believer in piracy, I really don't see Steam as a threat in that regard).
tl:dr. Steam is so successfull because of the services/sales they offer, not because they have the securest or strongest DRM. (Which is actually quite weak).