My point is that there are dozens of indie games on Steam, (on the indie section, 70), so being indie should not be a problem
70. Now compare that to how many games there are for sale out there. BigFishGames releases multiple downloadable games EVERY DAY. 70 is tiny.

It is not impossible for indie games to get onto steam, no. Obviously, some do. But there is NO GUARANTEE that any game will get there.
hpapillon, the game gates probably have at least some relatively objective means/standards for accepting games, although i have to agree that game play and graphics have some kind of subjectivity. These big game portals can't rely on subjectivity alone, and its a lot of money in stake (english is not my native language, but i think the expression is correct). They want to sell games and have profit, so i believe they have good will, but with quality. What is quality for them, is what we are discussing here, and again, no offense , please, to anyone. I don't believe in this case in any conspiracy or favoritism, really (except maybe for games made with game maker, read next). Doesn't make sense from a business point of view, at least not for the indie or casual market.
What they care about is what sells. But graphics and running speed don't determine that. Have you actually dealt with any portals, or talked to anyone who has, or read Steam's instructions for submitting?
One thing many of them will first ask is "Are we already selling any game that is similar to this? If so, how well is it selling?" If they have a similar game that's a smash hit, they will be keen to get a game that's like it, in the hopes of it making more sales. BFG, for example, is thrilled to get just about any Hidden Object Game because they've been selling like hotcakes for the past year, even crappy ones. But if a previous similar game tanked, then they may not be interested even if the new game looks great. It might even be a great game but a bad match for their audience.
Steam, otoh, is much more picky about what games they accept and has been known to turn games down because they are similar to a game that's selling okay but not blazingly hot, claiming that they already HAVE a game like that and they don't want a new game competing with it.
Another way portals determine what games they think will sell is by whether people have actually requested that they carry it. I had a game rejected from BFG (because they figured no one would buy a game full of reading) that they later turned around and carried because players were complaining that they wanted to buy it. Similarly, if ENOUGH people beg Steam to sell something, they'll try to sell it no matter what it looks like, because it appears to have a built-in audience. If you want to buy a particular game on Steam, don't write the developer and ask them to put it there, write Steam and ask THEM.

And another way STEAM determines what they want to sell is by public buzz. They request that applicants send in mainstream reviews and news articles talking about your game, because if your game is a hot property, they want to sell it.
These factors can override their personal tastes.... but if you don't meet any of these criteria then yes, it comes down to a purely subjective choice.
And maybe for Steam specifically, being made with game maker might be a problem too (but i can't prove that), for more than one reason i suspect (speed, easier to hack, no respect/being viewed as intrinsically for/to noobies, etc).
... once again, this sounds like you've been spending too much time reading the GMC and not dealing with the rest of the world. Why on earth would they care about most of those things? They'll care about speed if the
particular game you've written can't run up to scratch, obviously, but nobody buying the game is going to know what it was made with, and most of them won't have ever heard of GM anyway.
They're more likely to care about the game being too HARD to hack, and by that I mean - can it integrate with steamworks? If you can't interface with their wrapping/DRM then they can't sell you no matter how good your game is. There are a lot of tricky details that many game developers may need to recompile stuff for, and GM users may be totally unable to. If you can't hack your own game enough to make it work, game over.
Unfortunately I have no idea if it's possible to integrate GM games with steam because I don't think anyone's ever tried.