I don't see why there would be so little price difference between the V2 and V3 <snip> Seems like there is very little value placed on a good A/D product.
Three primary reasons, I think:
<1> All-in-one devices. As the all-in-one devices have gotten better and better, there's less desire to schlep around more gear when one may achieve 80-90% of the same sound quality in an all-in-one. I know I've succumbed to this one, as I traded out my V3 > HD-P2 for a 722. I still prefer the V3 pre/ADC sound, though. Part of the reason for me was that for 4-ch recording, it was just too much stuff to schlep around. I might very well go back to V3 > P2 if/when I decide to stick with strictly 2-ch recording again. However, the fact that the V2 still sells like hotcakes goes against this theory, which takes me to my second thought...
<2> "Conventional wisdom". A few people have posted - and many others repeated, sometimes without even owning one - that the V3 ADC was "weak", "thin", etc. I see it happening a lot around here. Someone or some small group of people decide a piece of gear isn't right for their ears, and all of a sudden many others are touting how "no one likes X", or "most TSers prefer X", or "X sounds weak and thin and <insert negatively-toned adjective here", etc. Of course, it happens in the reverse, too, with fluffing.
<3> Taste. 'Course, it could just be that people prefer the sound of other ADCs over the V3. It seems to me a lot of people like a bit of a "hyped" sound (very difficult to explain, so I won't bother trying), so it's no surprise the very natural sounding (to my ears) V3 isn't as popular. As someone who thinks the V3 ADC sounds better than nearly every portable, affordable ADC I've heard (with the possible exception of the Mytek)...my final thought is: there's no accounting for taste.