Just my guess: if they start with airless planets first, that means that flying into planets with atmosphere is going to require more work. Why would it require more work if you would just push a button and taken down? So, I think you will actually be flying down, otherwise, they would support all types of planets.
It takes a LOT more work for Frontier to release planets with atmospheres. Thats it really. Planets with atmospheres, or even moons, will have things like weather... clouds, just think how hard it is to do decent clouds in realtime 3D. Atmospheres planets have more erosion, because of rain, they have rivers, lakes. They can also have native fauna, which would mean some kind of procedural creature systems, to generate sea, land and air animals. Ouch... Also you have plant life, so again, procedural grass, shrubs, bushes, trees etc.
And then you can have intelligent life, with different levels of habition, from a few small mining towns or scientific outpost, all the way out to planets with 15,000,000 peeps there, with mega cities and star ports.