If there is a valid reason other than "who cares, it works" for using 12 MHz I would like to know it.

1. Using a 12 MHz crystal gives a performance increase over 11.0592. One tradeoff, however, is increased power consumption. Years ago I was concerned about making sure the SRAM and EPROM chips were fast enough, but now that is not an issue, as the parts keep getting faster (and cheaper!)

2. Timing. I have done a few applications with variable-speed motor control using the PCA timer. On a standard (12-clock) CPU, one clock equals one microsecond. When I had a board with an 11.0592 MHz crystal, I had to use a spreadsheet to convert times to reload values. Instead of a reload value of 1000 for 1 millisecond, it was 922 (actually 921.6, but the error was determined to be acceptable.)

These are not right and wrong choices, but design considerations. In the end, both variable speed products work equally well. It was just easier looking at the numbers and watching the 'scope when the timer reload values were in microseconds.