They've got history, so to speak. In the past, there seemed to be some kind of understanding that in the off-road sector Yokomo was responsible for 4WD buggys while AE concentrated on 2WD. With regard to team drivers Masami used to drive AE 2WDs and the AE guys ran Yokomo in 4WD, e.g. Mark Pavidis won a worlds with a YZ-10.
Yokomo has been the Japanese Associated distributor for a while and they seem to see no reason for changing that. Unfortunately, that does not seem to be the case the other way around (I don't know of any support for Yokomo from their long-term partner in the US), but given some time, A-Mainhobbies may be able to get it right.
The cars are definitely individual products, but as many models are similar these days, some parts may be exchangeable between various manufacturers.
IMHO Yokomo products are far superior compared to AE's stuff; at least I was not impressed at all with my SC10 and the twitchy B44 I was able to test for some laps...
