Yes this is a little known business secret. There are two types of sales. High spike sales and long term sales. The majority of "AAA" publishers focus on big investments, high risk, and hopefully high payoff style of game sales. They want it to sell as much as possible in two weeks, and if it doesn't it's a failure and never given a sequel again. Unless its sales fall under borderline in which case it might get one more chance.
However some recent studies have revealed a new factor in sales of video games "stick" factor. Some video games have high sales retention past two weeks. Some can sell very well over a very long period of time. However the AAA hotshots think this is invalid method of running a company. If your not making as much money as possible this instant your company is dying. Many of those old "AAA" companies are now dead, and many more are dying. A few are starting to to realize.
A third factor is that games don't need to be super big budget insanity "AAA" all the time. There is a huge market for moderate hits, and because the aaa developers don't make them a bunch of upstarts are now changing the playing field by making games with a smaller budget and more unique setting. Which in turn allows them to make bigger games as they find more success.
You'll find many of the best PC games have high "stick" factor in their sales. Which is the highest factor contributing to steams success other than its sales, and community. I'm not surprised at all. A lot of these companies who figured it out wouldn't want their secret of success getting out. While the old dinosaurs are dumb, blind, and stupid they do pack a mighty wallop if they ever caught on. Look at EA, an old dino that can adapt. Sickening as it is to say it has successfully transitioned. Now can they make it last? Perhaps, they loath the change. They didn't embrace their change but had to do it because necessity dictated they had to because of Steams growing rivalry. Now they run Origin which they pretty much have to do or else it could mean long term disaster.
As more services like Steam appear the majority of users will most likely congregate around the largest, oldest, and most successful services. EA got in on the game just in time. Things like uplay will probably not see so much success since they don't offer anything the other two don't. This last part is speculation on my part given everything I have learned.