Not really, I've used both and they are quite much of a muchness. It's not the base resin that makes the difference, it's the way it is formulated. Some primer fillers (like Duratec surface primer or Scott Bader Primecoat) are intended for pattern surfacing work and so have been formulated to polish up well. Regular 2k polyester or urethane automotive coatings are not intended for use as a top coating, so they haven't been formulated to retain gloss. They will all sand easily though.
The thing I like about the polyester based pattern coatings like Duratec and Scott Bader is they are quite flexible in their application. Not only can you adjust the catalyst percentage to adjust cure times, but you can also mix the coatings to adjust your gloss level. So you can either use straight primer and polish that up and that will give you a reasonably gloss surface to mould from, or you can mix in some of the high gloss coating (Duratec High Gloss Top Coat or Scott Bader Glosscoat) to give a higher level of gloss whilst still maintaining good primer filler characteristics and sandability. The more gloss coat you mix in, the better the gloss and the less primer filler functionality the coating will have.
That degree of flexibility is just so useful when pattern making.