I would say that Shinobi Girl are somewhat, highly improved step from Angel Girl so it boom out quickly to its sell rate where that very moment have multiple download spread out like a wild fire.
While Witch Girl are also improved in certain degree but its demo would high likely feature the same gameplay as their previous one, so some people feel rather blended for what they can expect, all new set of animation, changes in scenario and character but apart from that would basically still the same --- rendered Witch Girl not cost enough impact as much as when Shinobi Girl releases, they still have a good sell rate by itself quality tho.
I guess Kung-Fu Girl and Warrior Girl would fall into the same category, its sell rate wouldn't be boom out as much as its previous creation but will still sold out well by its own quality.
If we compare with Nekonomicon or Ayura Crisis, in which game style and its quality are pretty rare in this time. It's no doubt, cause huge impact up on it release and sold rate taken up even on top chart of current [ACT] label in DLsite quickly then I even relies.
At the same time, many Act game tent to have 'quality in certain part' but 'highly lack playable value' would also have its favorite rate highly conflict with sold rate when its release in which people would goes for its art and CG rather then game itself, if it also combining rule to unlock CG within while game are not even that interest to play for at least, to gathering those shiny CG, its sell rate would keep diminishing even more faster then when it freshly release, people would just wait for savefile to unlock stuff they want, or find CG set somewhere else without bother playing or buying their own.
Imaging KooonSoft try out a new genre with his current skill for something like Castlevania-ish, Platformer, Run'n'Gun or Beat them up or any other type that not One-way-Sidescroll they would cause some huge impact no doubt.
