I think its a style/era thing.
When I first got into psy (or i suppose people would partition it off as "goa" these days) i was loving the deep, deep subbass. Check for example Cosmosis - Cosmology -- there's one track on there in particular which is written in such a key that when the subs come in they are deeper than just about anything ever. Properly throbbing sub-bass without a doubt.
Lately though I have noticed quite a few releases with a "thin" sound overall. Gataka - Drop the Mask was the worst example I found last year - it sounded like it had been highpassed at 80hz. Ugh - rubbish - I deleted it instantly.
My guess is this...
1. E music. I dont take E, so I've no real idea, but I've heard rumours that sub-bass and E dont mix brilliantly. Basically there was this thread on Isratrance with people saying they hated deep bass because "it slowed the music down". I nearly pissed my pants laughing but several other people agreed claiming when they were pilled up they associated low frequencies with being dragged down, higher frequencies with floating away. So as commercial/full-on psy has become more E music and less mushie/acid music, it seems like releases have been having less and less bass
2. general trends in the musical style. kinda related to the above, I guess, but I notice the bassline in modern full-on doesnt really act in the same way that basslines used to. ie its not really there to provide chest-shaking frequencies at all - its there as a rhythmic/fast/driving thing (just think of the whole 16th note vb1 cliche - again gataka is a pretty 'good' example). The old deep subs used to come from the
K-B-K-B-
routine, which seems unfashionable these days, partly because its meter is half-speed compared to the 16th note efforts, I suppose. But this arrangement gave plenty of space for a very low bass, partly because it was always halfway between kicks, partly because each sub-plonk had a full eigth to die away in. On the other hand kicks back then were freqently quite high-- I think now perhaps are more keen to get weight on their kicks, and this combined with the 16th approach to basslines, doesnt really leave as much room for the bass to contain strong LF energy
3. general trends in sound + mastering-- partly related I guess to the previous point, it was very noticable to me last year that a lot of albums these days have quite, erm, distinctive overall sound and mastering. Protoculture - refractions would be one good example. Really squashed as fuck in the mid and upper ranges - bright and crisp and hard to the point of being quite "brittle" - almost verging on the whole artificially shiny and loud "radio" mastered music, ie pop. imho totally overmastered but thats another story.
So, I would say in certain styles of psy the sub-bass has decreased yes....