AFAIK most lower-end routers have pretty generic firmware (with their logo added) as well. Maybe paying a no-name firmware sweatshop to tweak some reference firmware is cheaper than tweaking OpenWhatever.
Do they even have enough memory for OpenWRT? Maybe DD-WRT.
At the low end, I'd think the chipset manufacturer would do most of the software work, then the device manufacturer just cosmetically tweaks the reference.
