This is capitalism. The superior, best product will make the most money in the short term. Steam has done that. Now they are also achieving a form of lock-in, due to the fact that its incredibly convenient to have everything in one place. The bottom line is that if Microsoft had done this first, we would be complaining about them rather than Valve. If you ask me, I am REALLY glad it was valve, rather than Microsoft that figured this out.
Is Steam perfect? No. But before you bash Steam, ask yourself if its really doing more harm than good. In my opinion, it has done, and is still doing way more good.
Why Steam being dominant is the best for the future: The best thing possible for the industry is for one delivery platform to have dominance in the masses, simply for ready access to the consumer. Right now, it enables small developers to have a direct pipeline to the market. This is the ONLY way that developers can break free of the shackles of publishers right now. Wild indie successes will lead to developers being able to self-finance a lot more, which is something that was completely unheard of five years ago. This is only possible if there is a delivery platform for these games that can reach a large segment of the market. Publishers such as EA will lose their iron-clad grip on the PC market, and we will see a lot more blizzards and bungies arise in the next 5-10 years. Which means we will see far more original, well-made games on the PC. Its not fanboism, its economics.