I may be missing something, or over generalizing - and pardon me if i am as i'm not a chemist - but are you sure Tom? Either way i was just trying to paint a picture, and didn't set out to divert the discussion. None of the issues are blockers to using epoxies in most cases (one of my favourite adhesives), but the liking for heat, need for accurate mix ratios, need for choice of the right resin system, oxygen inhibition at the surface/wax/oozing of excess leading to the possibility of difficulty in bonding over a previous coating of epoxy are all pretty characteristic.
So far as i can recall most of the overbonding difficulty in standard resins arises from the inevitability of imperfections in the mix ratio, it's the UV/light curing variety that suffer most from oxygen inhibition. The wax issue relates primarily to laminating resins.
There are differences between formulations and resin types, but this link for example discusses the inhibition issue as it impacts UV curing resins (see from about eight posts down), an epoxy makers comes in at the end: http://forum.surfermag.com/forum/ubb...te_id=1#import Googling 'oxygen inhibition' brings up all kinds of tech papers on the topic - its an issue with many types of polymerising resin systems as well as epoxies.
Different strategies get used to tackle the re-bonding issue in different situations, and it's certainly got to be a minimal issue inside a sealed glue joint since it's unlikely to be re-coated - but it can be very significant if trying to recoat externally to smooth a fillet, or when adding a second coat to further seal a surface or something like that - especially if you end up cutting back through the top layer.
One essential difference between an epoxy and a polyester resin cure is that the epoxy is a stoichiometric system which to my only very basic understanding of the chemistry means that each molecule of cured polymer requires a given number of molecules of each of the resin components. Add a little too much of one or the other, and the surplus simply doesn't get used, and as well as producing side effects like the tacky surface mentioned the properties of the cured material rapidly disimprove. Polyester is different, in that it's a catalytic cure. The hardener by its presence triggers a cure in the already present resin. Adding extra speeds up the cure, but it makes little difference (within reasonable limits) to the final properties of the cured material.