Yeah, chemically, resin is pretty different from thermoplastic (e.g. abs, nylon, PLA). It’s more similar to two-part curing or moisture curing room-temperature-vulcanizing polymers, like paint or shellac.
The intuition here is that for things like acrylic paint or latex wall paint, you can thin or clean these while they’re wet with water, alcohol, or whatever the recommended solvent is. But once they’re dry and hard , the same solvents will no longer dissolve the paint.
That’s because what’s happening with modern paints is not so much “drying” (where there are solids dissolved in a solvent that then evaporates, leaving a coating of the solid behind), but they are polymerizing. That is, undergoing a chemical reaction (for single-part mixtures, often times moisture in the air drives the initiator like UV drives the initiator for our 3D printer resins) where the solid is a different compound than the liquid, and thus has different chemical properties.
Modern paints also do have solvents and dissolved solids to improve the features of the paint. High-end industrial use photopolymer resins have these as well (which would be sold as resins that include VOCs, volatile organic compounds, which generally refers to a solvent). The resins sold for smaller scale hobby use are generally labelled “no VOCs”, which is what you want if you’re not printing in an industrial setting.
The blog and Instructables articles about resin formulation written by Autodesk are very instructive on the topic:
http://spark.autodesk.com/blog/embers-resin-now-open-source
http://www.instructables.com/id/How-to-tune-Embers-print-settings-for-new-resins/?ALLSTEPS