Generally, my reason for loving Steam is the convenience. I grew up in an area where there was no EBgames and no real convenient way to order in something fast and convenient, so I missed out on a lot of titles. Even to this day with consoles or handheld it can be hard, if not impossible, to track down some games. Piracy in the late 90s and early 2000s was legitimized simply because you could not find a copy of the game you want sitting on a shelf in the store, or order it in easily. Fast foward to today where if you are patient you can get a game pretty cheap on Steam Sale (or Origin/GOG/Amazon) and its an embarassment of riches. Gabe has the right idea that piracy is more of a question of service and market realities rather than cheap skates, and I am sure he has made legitimate software users out of a lot of people through Steam and its service. I feel that for everything Steam demands (ie online verification, license only software model), Valve at least gives something in return to make the whole thing as convenient, smooth, and pleasant as possible. But the core attitude of software as a service, and that service being as pleasant as possible for the customer being the core of Steam along with insane prices is what has kept my business.
Origin's main short comings with me are that EA made many of its flag ship titles (read: Battlefield 3/4 and Mass Effect 3) non steam in order to promote their service, but also that I've had a lot of problems when it comes to how clunky the Origin point of sale system is. I have litterally gone to buy something on sale, get an error or other weird things going on, and after ten minutes of mucking about I simply threw my hands up and said "I give up, EA doesn't want my money". Customers should never get to the point where it is too much of a hassle to buy something in your store, especially pre purchase. If you are trying to convince somebody to buy something, you should make it extremely convenient and pleasant for them to want to pay you for a service even if its harder for the company, its the reason why you do not see body scans and TSA like searches at a super market check out lines. Its better to have a few people get away with shop lifting than treat every legitimate paying customer in your store feel like a terrorist in the hopes of making the bad guys have five whole extra minutes of inconvenience, and its better to spend the extra money to almalgamate all your studios' registration systems and/or pay walls than to make players jump through endless hoops. In EA's defense, Origin has become much more tolerable in the last year and hopefully they are learning some lessons, and if anything having another big boy digital download service should keep both Valve and even console only DL services honest as competition is always a good thing.
TL;DR version: Steam is convenient and often cheap. I like convenient and cheap. If Steam DRM bothers you, there are other services out there (like GOG.com or Humblebundle) to suit your fancy that are competitively priced, so go nuts.
