At least you are consistent. i was wondering the other day about why so many seem to use cotton/poly sheets when it seems like so many also will only use 100% cotton in the quilt itself.
I am not a purist, so I don't mind using poly/cotton, esp. on my charity quilts to the poor. I figure if the quilt is used for 2-3 years, then that is good....so a poly/cotton sheet (used) is fine.
But I also had some of the same thoughts about why people will spend all this time on the front and then use whatever on the back.
Since I use "whatever I have" on the front as well, I do scrappy backs... :)