How come the font is 8x8 pixels instead of 10x10?

The OHRRPGCE font is 8x8 for historical reasons. The font-drawing code was originally written for the game Bob the Hamster VGA, which uses 16x16 maptiles and sprite tiles.

Although 10x10 fonts might seem more logical for the OHRRPGCE because of the 20x20 maptiles and walkabouts, retrofitting the code to support other fonts sizes would be a fairly major operation (which is not to say that it could never happen someday)