So how would you store wheat, rice, beans, etc? I've yet to hear that it is unsafe to do this for long term storage. Hell the mylar bag people just throw oxygen absorbers in and seal the bag. I'm not disagreeing with you that stuff could get in though. It just caught me off guard kind of like a "Don't play with a knife because you might cut yourself" comment.
Vacuum sealing those items will extend their shelf life dramatically over just leaving them in a box or bag as they come from the store. The trouble is that they have been exposed to air, moisture, your counter top, etc. before getting into that mylar bag or your foodsaver bags. It's like those big cans of freeze dried foods - once you open them you'd better use them all up soon because you have introduced air, humidity, utensils, and whatever else into their previously (assumed to be) stable environment inside that can. Frozen items are different because it is the freezing that does the preserving while the vacuum sealing of the frozen food just keeps out the air and moisture that causes 'freezer burn.'
I hope this makes sense? Maybe PistolBob can elaborate or clarify better. Vacuum packing your rice and such is way better than just leaving it out exposed to air but doesn't always guarantee it'll be good 50 years from now.
And what's the best way to store them? I have no clue. Anybody?