Do you play shooters? I have found that with the indented sticks, it's harder to get a smooth progressive movement because at some point, your will either be moving the stick by touching the edge of the stick to when you might be sealing it with your thumb (i.e. when you move the stick towards the thumb as opposed to away from it).
If you have a convex form, this happens less because moving the stick towards and away from your thumb gives you a more or less consistent hold of the stick.
Don't get me wrong, I find the DS4 to be by pretty much all accounts a better controller than the DS3. That's my only real gripe with it and this little detail (while you can get used to it) is quite noticable when you play shooters competitively (especially twichy ones, like CoD or BF4) where every micromovement on the stick will have a larger impact on your precision on screen.