I wasn't referring to the product description, I was referring to the application instructions that are on the can. If they require a primer to put it over oil based product, that's where they would say so. This isn't an unusual thing, it's fairly common and it would be pretty dumb for BM to not state it, if it's required, will cause failure, etc.
I would agree with that, but it wasn't me that said that primer is a must when going over oil based. If it's typical, weathered paint that is otherwise sound, then you can go over it with latex. If it's chalky or has other problems, then that is an issue with any kind of base.
How many paint cans have you seen of solid stain topcoat product or similar, where in the application instructions they only address going over bare wood? The vast majority of the product is used going over previously painted surfaces and again, in the application instructions BM doesn't have any restriction on using it over existing oil based paint.