I couldn't remember any shows that centered around postal workers. Seinfeld had a regular character and a few episodes about the postal system (but then that show had an episode about almost everything). But it did make me think about "Get a Life" which starred an adult paperboy http://thetvdb.com/?tab=series&id=76500&lid=7
Construction crews was the same, I could think of several shows off the top of my head that center around the "idea" but none that landed right on it. There's Arrested Development which centers around a land development company (but really isn't about that all that much). Home Improvement, which isn't actually about home improvement and is more about a guy who has a show about tools. You said "show" but I'm guessing you meant sitcom/drama based on context so that rules out Extreme Makeover: Home Edition, since that's really reality-vertising. No worries, I'm sure someone on HN will figure this one out.
A truly gifted writer could make a show about almost anything interesting
I totally agree, including a cop/doctor/lawyer show. :o) One of my favorites was "Ed" on NBC ... first season only, though (http://stuckeyville.com).