That's one way to do it. Another way is to own your own club, or manage one your friend owns. At the club I managed in Colorado, we had our sound system hooked up to a computer that accessed the internet. We had a streaming music service and we'd use that most of the time to build genre playlists at random. We could also look up requests and drag and drop them into our current playlist. We also purchased a bunch of MP3s so when the internet went down we still had several hours of music we could play. There was no crossfading, no beat matching, not even building playlists with rising and falling energy. We just pushed play and let the computer do its thing. Even had two seconds of dead air between every song.
Now, three other clubs in town hired pro/semi-pro DJs with their own equipment, music collections, and a buttload of talent mixing, crossfading, and beat matching. One DJ in town even spun vinyl and he was damn good at it plus he did a lot of his own remixes. Oddly enough, those clubs struggled every night with very low turnouts while our club flourished.
Why? It's not always about the music, though sometimes it helps. What we played was better than the other clubs (we catered to most requests, no matter how much we personally hated the music) even though the other clubs played their music better. Our sound system kicked some major ass though and that definitely helped. And we had a TON of lights. Mostly though, it was all about atmosphere. Music is part of that, but not all of it.
Anyway, I have no idea what point I was getting at when I started. It's past my bedtime and I'm rambling. I guess it's that DJs put a lot of stock into the music and their art because that is their life, but honestly, most people in a crowd couldn't give two shits as long as there's a beat they can dance to and the alcohol is cheap and plentiful. Sometimes it is as simple as pushing play on an iPod with Pandora and walking away.