Dr. Hauser, is this because the larvae are all so alike, or is it because nobody's ever really bothered to photograph and/or describe the various larvae?

All of the above ;-)
Diptera larvae are relatively similar, but when you look closely they have a lot of good characters and it is normally not a problem to identify a larvae to the family level... It is mainly that only a few people ever worked on larvae and collected and reared them, and then made GOOD and DETAILED descriptions.... Although identifying larvae from photographs is very difficult because the structures you need to see are very small (the anterior and posterior spiracle, the mouth parts etc), so you need a very good microscope in the first place...But some larvae are very characteristic and easy to place... your larvae has very striking color patterns, and that should be a good hint for somebody who knows larvae very well...

a nematoceran of some kind [crane?]; often see them but never cared enough to find out -- now is the time... ceratopogonid larvae look similar, too

some kind of larva then, most likely? I thought even in immature forms (like caterpillars) that insects showed some legs...not always?

Can't go larger (already 560 px wide), but I'll crop pictures bigger so you get segments of the articulated, worm-like, critter thing. :)

Found in a rotting old bit of stump.

You can upload larger images, you just won't be able to see the larger versions. Only editors will be able to see them.

If you do crop, more people will be able to see the cropped versions. So this may be the better route.