1. As vishaldpatel notes, the pattern resembles meditative mantras. However the mind reacts to religious chanting, "trance" resembles that and invokes similar focus to the exclusion of other distractions. Indeed, we call the music "trance" for a reason.
2. The music does not demand attention to itself. Most other music is created with a "drop what your doing and pay attention to ME" sense, and we go to concerts and pay good money to listen to such music for what it is as the center of our attention at that time. Dance music derived from ambient origins creates a beautiful backdrop to something else, driving away other distractions and setting a pleasant environment for whatever we really want to do; most of it is created for, well, dancing - but the style where the focus is on self & moment, not on music or others & events.
In our culture, very little else combines to create this audio backdrop combining meditation and high energy. Most instruments demand the musician(s) focus on a full performance, and hence expect (hope?) the audience to give similar attention - the antithesis of what we're looking for here. Even "minimalist" acoustic[ish] music like Philip Glass & Steve Reich, which resembles "trance", requires an intense single-performance effort & focus of the performers, giving the implication to the audience that similar focus should return the favor.
Electronic music allows lots of free-running loops, zero-effort samples, edited-to-perfection sequences, and time-unconstrained editing after the fact - to wit, it's not created live, not intended for live performance, and the artist has no attitude of "I'm not utterly focused on perfect end-to-end performance of this, so I don't expect utter focus of the audience". Acoustic meditative music heads this way, but involves the performer in the focused activity; music isn't an ingrained part/consequence of coding.
Upshot: electronic music lends itself to creating coding-productive music. We'd like such music from other sources, but nothing else lends itself to producing such high-energy long-run content without demanding the listener's attention.
Interesting that the reasons given here mostly also apply to game soundtracks as well, which is mostly what I listen to while coding. (Overclocked Remix has some great compilations if you are looking.)
I suspect game soundtracks differ from film soundtracks in that they're the backdrop to something that's still interactive, but I'm not sure how that comes into play.
Music for 18 Musicians is usually my first choice whenever I want an hour of uninterrupted productivity. The piano and mallot lines are like a rhythmic propulsion system.
I am a music addict and can (and do) listen to almost all genres of music during coding. But a consistent pattern is that I rarely listen to _new_ music while coding. What happens to me is that when I am really concentrated, I start listening to one album over and over to make sure that the music doesn't surprise me or force my attention. Sadly, its also a way to kill albums for you real quick :).
At my workplace we have a contractor that listens to hardcore speed metal while coding. The really angry kind...
It is hilarious when you realise how calm he is working on the project, completely opposite to what the music is. My colleague prefers listening to old school rock, and my boss (coder as well) listens to classical music.
Definitely a lot of different tastes out there.
I personally am a trance/techno/electronic/dub step/vocal trance kinda person.
Based on the comments here, electronic music (whether it's ambient, trance or dubstep) appears to be the assumed genre.