I expect that they are very much a dual purpose scope and so used for both visual and imaging.
The ED are very good and often more then adaquate for imaging. The main aspect is that the user understands that there may be some CA on objects.
Something like M81, 82 and M101 and M33 and Rosette Nebula will all be fine as they are not singularily bright. Whereas the Horsehead with Alnitak is likely to show some CA.
The makers put APO on the front of ED doublets and they put APO on higher quality triplets. People read as far as "APO" and expect the same performance from both and expect the higher performance.
If you read the specification of most ED doublets somewhere in there it will say "Virtually eliminates CA" or very similar.
There are lots of good, very good, images from ED doublets. I suppose the factor is the margin of safety and by rights you should be safer with a good triplet. However they cost and these days a good (has to be good) ED doublet gets very close.
People use everyday achro's for some imaging, and again why not as long as the limitations are understood.