I do drink some wine from the store and from commercial wineries. It is good to compare against my own, or to drink varieties I don't make. It's always fun to be drinking a $19.95 commercial winery bottle and realize my batch at $2.50 a bottle or whatever is every bit as yummy, so therefore could conceivably bring $19.95 in the marektplace.
Commercial sampling also gives me cues I want to strive for in my own wines. For example, I am still in an over-yearlong pursuit of the mouthfeel of a $6 (at Wal-Marts in Illinois) Illinois Cellars Velvet Red.
Some of you have gotten PMs from me about that quest!
I'm still not on it, but I am experimenting to try to find something close.
I have a suggestion for Keith along these lines, as well. I'll email it.