Have you asked the retailers what differences there are in the two product lines?
Good idea. I've send some emails and it depends who you ask... Those that have two obviously different lines usually say the differences mostly are the koshita (soft for aikido, hard for iaido/kendo) and the length of the himo, which is longer for aikido to be tied in the front. The last difference being the length, kendo ones being sligthly longer than aikido ones.
Others tell the main difference is the color: black for aikido, blue for kendo, but otherwise are basically the same.
That said, interestingly, I just realized that I've done aikido for years with a kendo hakama: hard plastic koshita and the himo tied in the back... So, I suppose this answers my question: there are differences, but one can basically practice aikido with a kendo hakama without noticing it if not aware of the differences...