Well, I mean... The loudness war isn't a joke. A lot of electronica producers - especially those who also make more uptempo dancefloor music - want their tunes loud. Are you saying that you think a lot of psybient is mastered particularly loud?
From my experience, it's all over the map. Some is quite quiet; others times, the songs are mastered so that the kicks and snares are clipping substantially on every downbeat (which is something I associate with massive dancefloor tunes, albeit ridiculously loud ones).
I'm almost more surprised these days when people release tunes that aren't that loud.
When I do a chill set, I work with a lot of loops from acid jazz and neo soul stuff... some new, some older. But, working in Ableton, I'm turning down some clips a whole lot just to get everything at a consistent volume. Usually not more than -6 db or so, but that's pretty substantial.
Although, now that I think about it, some of the psybient tunes I have currently rigged up for downtempo sets are the clips that are turned down the most, so that might support what you're noticing...