Latex paint peeling off oil based paint. How do I apply a new layer of paint?
Painting over a glossy oil paint is indeed different than painting over an oil primer. I just came from a customers's home where the seller did the former - you can literally pull sheets of the paint off the trim. Maybe there are better latex paints that tend to adhere more strongly and you can get away with putting them over oil, but I'd never do it. 

Don't take the chance. Either stick with oil-based paint on trim that already has it, or sand and prime first before switching to latex.