I tried to find an educated answer but there wasn't one. Most of our 25 ct boxes allow for 12 with a cedar block in one row & 13 in the other row.
As far as Domestic cigars:
Padron regulars are 26 ct
Padron Anniversario 25 ct
Gloria Serie R 24 ct
Cohibas 25 ct .. Tubos 10 count
Fuente Chateau & 858 20 ct/ others 25 ct
Most Macanudo, Montecristo, reg La Gloria 25 ct
etc etc..
There are several makers w/ 10 count & some with 12 count. I have no idea if there is any reason.
I'm sure that didn't help a damned bit

but there is a really cool website I found called Cigar History while I was looking.