Hmmmmm.....
This was my experience as well. We used the Rustoleum Epoxy kit we got at Lowe's when we had our new garage built in 2008. The surface is still in great condition, no chipping, peeling or fading. Still completely waterproof, too, which we discover every time we have snow and it falls off the vehicles and just pools on the floor instead of soaking into the concrete.
I think this is the case. I'm guessing those who had problems probably put it on an old slab and it may not have been clean enough. We not only put ours on a brand new slab but we also followed all the instructions and washed it with the acid-etching material before we painted on the coating.
One thing to be cautions of, as I said above, it will pool water and that means if the garage/shop gets below freezing you can have icy spots. Our detached garage does sometimes get them. Still, it's super easy to clean up, and I've even spilled oil on it (while changing oil on one of the motorcycles) and cleanup was a snap.
If you do this, invest in a squeegee for water. A drain on the floor might be a consideration, too. I kind of wish I had one.