Not sure, I have had Commanders with almost every nation so far, except Minors. Plus I rarely see much of an impact on the battlefield with them anyway..not sure what you get for them...sometimes they have negative impacts by their details?
After spending the last 3 hours fixing errors, that come with the games commanders script, I now know the main reason why, you don't see any impact off having a General attached! The truth is, most of the scripts associated with the different commanders, that come with the game, don't have their individual stats activated, meaning that the Attack / Defence factors, that should be boosted by having a General attached, are not calculated during combat, so in effect your right the commanders do diddly squat. That is the bad news, the good news is this has now been rectified, because I have went through each and every commander in turn, and activated their stats, so now they do assist the unit they are attached too.
Have seen where the nearby units of a commander show stat changes beyond their normal stats. You mean to tell me: All this time This was not actually true! I hope what you have discovered, is corrected in the upcoming 1.40 patch...