I've always questioned the effects of the environment on a air filter's media over time.
I know this is *not* an apples to apples comparison, but think about what happens to paper if left outside in the elements over a period of time. Even if you keep it in your (detached) garage, per say, it seems to weather somewhat. It may not be in direct contact with rain, snow, sun, etc, but the temperature swings and humidity levels seem to cause deterioration none the less.
I would imagine the same would happen with air filters as well. I will assume the media has been engineered to handle these things, but it is still cellulose, yes?
I'm all for plastic-wrapping these types of filters for storage before purchase. Most of the time they are in a (hopefully) climate controlled store before you recieve them, but it would add a level of protection I would appreciate as well.
Air filters are one thing I don't go cheap on, as I keep them on our cars for a couple/few years and many, many miles.