Unfortunately true. We'd have to redo the rules to allow for Dropships that cannot land, and give them a cost discount. But that gets into the fun areas of monitors.
It really doesn't. The monitor argument was about warships. Dropships, even with subcapital weapons are not warships. And the PTB were silly to not provide a compromise, because we know from small craft and dropshuttles that KF cores or booms are not required for realspace mobility.
Also true, but a space-only platform has to only work with a 15 psi different between exterior and interior pressure. An atmospheric-capable platform will have variable pressures between inside and out, and varying atmospheres it has to deal with. So instead of just designing airlocks to keep interior air in, the airlocks have to b able to handle potentially greater exterior pressure, varying temperatures, and the materials have to be able to handle different types of atmosphere.
I present exhibit A: the battlemech and tracked vehicle price formulas. They are identical. Battlemechs are able to operate in any environment a dropship can land. Vehicles (without additional sealing expense) can only operate in human livable atmospheres. The ability to handle a variety of surface environments is baked into the equipment prices. An autocannon incapable of handling exotic atmospheres might cost less than one that can, but it doesn't matter because nobody manufactures such a thing.
Reentry heating countermeasures depend on mass and to some extent volume, not on price and only to some components. Projecting structures must be retracted behind covers for aerodynamic reasons if nothing else. This potential reentry penalty does not apply to all surface equipment. Heatsinks, for example, are mounted flush in Battletech. This does not mean reentry capable dropships require more expensive heatsinks. Heatsinks are heatsinks. I present Exhibit B: the conventional fighter and ASF price calculations. They are identical apart from conventionals not having an optional omnitech multiplier. Anything that can be mounted flushed (which due to the absence of turrets on fighters is most everything) is, again, only available in reentry capable versions. As the cost of retractable turrets and covers for weapon bays depends on the number and weight of weapons it would be part of the gunnery control system costs, not a multiplier applying to anything else. If sensors and comms equipment require retractable covers (ASF sensors don't seem to) that would be part of the sensor cost or bridge cost.
The only things that can justify a cost multiplier that includes interchangeable components like weapons and heatsinks are labor costs. If anything these should be lower for atmosphere capable spacecraft because they can be built either on a planet with gravity and an atmosphere or in microgravity, whichever is cheaper, while void only spacecraft can only be built in microgravity. Things like infantry bays might justify a sealing and life support premium on spacecraft and submersibles, but that would be a difference in component price not a justification for a general price multiplier.