Prevalence of not-quite-seated frets.

This is sort of a follow-up to my previous post here about frets I found on my guitar that weren't quite flush with the fretboard, but that also weren't springy. I decided to check my other three guitars and found that every single one of them has a few frets I can get a .004 feeler gauge underneath, usually on the side of the fret closest to the bridge in the middle of the fret, and, again, not springy (the fret doesn't move under pressure). I thought that maybe it is just my guitars for some reason, so I went to the local pawn shop that tends to have a pretty decent collection of used instruments and asked the attendant in the shop if she was okay with me checking the frets with my feeler gauge. She said no problem so I carefully checked several of the guitars, ranging in price from $100 to $2000 and found that every guitar under $1000 had at least two frets that I could get my feeler gauge under. A couple of these were cheaper instruments in bad shape that had springy frets popping off at the ends, but most cases were similar to what I found on my guitars at home: frets that weren't completely flush with the fretboard, but that otherwise seemed solid.

Is this a quality control issue? Are sub-$1000 dollar guitars often leaving the factory with frets that aren't properly seated?