Is it normal for 8x10 photo prints to measure slightly under 8x10 inches?

Within production of paper based products such as photo prints, there are inaccuracies that are hard to avoid. If the prints are exposed on photo paper usually paper rolls are used which may already show these inaccuracies. Here you can find tolerances that are acceptable within an usual international paper size standard. I would guess, if your deviations are in the same range (about 1/10 in for comparable sizes) you have little arguments for a claim, but I would guess at least with local printers you could at least define some lower tolerances in advance.

There is even a bigger problem if the sizes are derived from a different unit system. In Germany we have a usual size of 10 cm x 15 cm, which may or may not be 4 in by 6 in, dependent on the manufacturer of the paper. In the latter case, it is a deviation of more than 2 mm on the longer side.

Usually the picture frames should be constructed with a bit smaller exposed area such that the border of the print is entirely hidden, but from my experience you can never be sure and have to measure in every single case. Disappointing.