I've become so used to this practice in grocery stores that I "do that math" rather compulsively when I see such labels.

I'll admit that the average consumer won't bother, but it's really not hard:

8\3 is 2, that's pretty obvious. So you're buying three items for $2.xx each, so $6 is allocated, leaving $2 unaccounted for. Again, three things, so you're adding 1/3 of each remaining dollar to the individual price - 2x1/3 is 2/3 or .66.

$2.66 per item. It's really simple math, but again, the average consumer probably just can't be bothered to do it. Part of the problem is people who have just convinced themselves that math is "too hard."