I agree with you that the inclusion or absence of a Neo improvement can affect buying habits of certain consumers in situations where 2 or more games are very similar.
What you're saying makes sense for informed individuals. In aggregate, though, people make decisions for a wide spectrum of reasons. Some aren't as devoted to a specific series as you imagine and could be swayed by buzz surrounding a product. Novelty generates that buzz, so showing something that couldn't be done before is one way to get press, attention, and thereby sales.
Why didn't any of the big francises you've listed just sit out the PS3/PS4 transition for a few years? After all, there were more PS3 owners by a long shot. In practice, PS3 releases don't get as much attention when there are fancier screen shots to show on the new platform. Plus Sony will throw co-marketing dollars behind something that makes them look good. Add in that early adopters tend to responsible for a disproportionately large proportion of software sales and the equation skews even more.
Last, but not least, consider the technical and artistic talent responsible for moving the industry forward. How are you going to keep your best people if you aren't going to let them push some boundaries with new hardware? It's not an all-or-nothing proposition. We won't see publishers or developers maxing out the new hardware or ignoring the base hardware but they'll start the progressive arms race to better visuals again and we'll see improvement in fits and starts.
Keep in mind that even if they do
nothing at all their titles will be running on faster hardware and will be far less prone to dips in frame rate on the Neo. That's the baseline and things just get better from there.