One other piece of information that would seem to point to some fighters being, at least inappropriate, if not incapable, for atmospheric combat comes in WCIV. I forget the exact context, but I *think* it is when you are in the ship selection screen, and you switch to the Vindicator. Either in the "Pliers written text" or possibly in a Pliers voiceover, I think Pliers says something to the effect of:
"The Vindicator might not have the staying power of some other fighters, but its the only one you can use for atmospheric missions".
Can anyone confirm/clarify this quote?
It does seem that many of the "atmospheric" fighters do have fairly aerodynamic shapes (Hellcat, Excalibur, Dralthi), but others have decidedly non-aerodynamic shapes (Ferret, Ekapsi), so I don't think one can conclusively argue that fighter shape is the deciding factor.
However, I would certainly imagine different technologies dominate a fighters performance in atmosphere versus in space, and as such, there are probably significantly different ways to tune a fighters engines, repulsor-whatever field, acceleration absorbers, targeting computer, etc., to be optimum for atmospheric combat as opposed to space combat. Very probably, since fighters shifted to a more space-based role, only the few fighters that are easiest to tune to atmospheric combat or that are most effective in atmospheres are so tuned, and hence while any fighter might (or might not) be able to enter and atmosphere and land, probably each side only relies on a few to actualy use to fight.