They're very picky about who submissions they accept. To be honest there is no rhyme or reason with their method. Some huge labels have been turned down by Beatport and some small unknown labels have done really well on Beatport. I guess all I can say is don't take it personally if they don't answer back, because it happens people big and small. Quality control is a factor that Beatport is going to have to rely on heavily in the future if they want to stay at number one.
If you're lucky and get an account with Beatport, it can go either way. If your music sucks or it's outdated stuff, it won't sell. If it's quality music and somewhat relevant to the time, it will probably sell. I have a buddy who runs a progressive house label on there, he no longer puts out vinyl but runs mp3s solely. Every quarter he gets a nice check for a few hundred bucks after paying the artists what they are owed. You can't complain about free money.
Oh, and anybody who says MP3s don't sell is full of sh*t.