Compression/decompression and edge oxidation are not theories, they're facts of life. Some alloys are more ductile and will compress more easily/dramatically than others, which of course leads to great variances. Some environments are more corrosive and will affect different steels based on their ability to (or lack of ability) to resist that corrosion, just as others have noted. So, depending on what the conditions are, you may well see some stainless alloy "air dull" more significantly than a non-stainless brother, or one non-stainless steel lose its sharpness more quickly than another non-stainless.
Easy things to do are:
1) Don't use much pressure when you sharpen. Unless you're having to hog off huge amounts of steel in order to repair major damage, just use a comfortable (couple of fingers worth) downward pressure, like you were crushing a cherry tomato versus crushing a walnut. If your hand is getting tired from sharpening, you're pressing too hard. Compression isn't the only problem--you're likely to end up removing more material than you need, because as the tension in your hand increases, your precision drops, so you end up making more passes to get the angle right and correct your mistakes. Also, you wear out your sharpening surface much more quickly than you would otherwise.
2) As knifenut1013 mentioned, the finish on the edge can affect how well it resists corrosive influences. Of course, for some applications, a coarser edge will serve better than a polished one. Whichever you have, keeping it clean between uses will help a great deal, and once it's clean after use (or immediately after sharpening) coating it with some kind of barrier to keep corrosive agents away from it will greatly slow its degradation. There are any number of gun-protectant chemicals out there that will work very well, but even a simple wax like clear shoe polish or chapstick will help a good bit. I've been using chapstick on knives for years when on hunting trips---skinning, butchering, whatever I have to do, and then clean the blade off, make sure it's dry (so you don't trap moisture next to the steel) and coat the edge with wax. My new favorite skinner is made of M4--which rusts like there's no tomorrow if neglected--and over the five days and four antelope that it went through in Wyoming last October, it was not sharpened or touched up once. The steel had great edge retention for the cutting chores, to be sure, but all that blood and snow would have turned it into a butter knife pretty soon if I'd let them, but I didn't. It's been sitting in the safe since then, waiting for its next hunting trip--I'll check after bit for curiosity's sake, but I'll bet you it'll still pop hairs if it won't quite still whittle them.
Just as a by-the-way, alcohol wipes are another outstanding accessory in the field. Don't use them for the principle cleaning as regular dirt or water will do that just fine, but as a finishing touch to remove any oils or moisture left behind. Follow that with a pass along the edge with some chapstick and it'll stay sharp a hell of a long time.
if not then you know you got more polishing to do 
