DJ's, A&R people, label managers that I know are picky as hell with what they spinn or sign. There are people who never miss the target because they spend a hell of a lot of time weeding out all the crap. It's a fulltime job going through all the released tracks online.
I actually did a count a while back, I noticed I could listen to around 500 mp3 samples of all different genres(electronic music) and only find about one real, long-lasting track that I really love. As good as the internet has been to spreading music out to the world it also has it's backsides because the digital scene has exploded in such a massive way and there is relatively little quality control online. Before digital shops you had record labels, record distributors and record shops, all checking the music before it ever got out to you. Now, in many cases people can sell direct to the digital stores so there is a redicules amount of clobber that is finding its way out there.