well, that's what i used to think also, i'm on my third hero for unrelated problems, but all three had random dropped calls plus very erratic reception.
I gave up, convinced telus to scrap my remaining 30 months and bought an iphone 3gs for the new contract price, i've had it for 2 weeks, i get full bars basically everywhere, including inside, not one dropped call either, i upgraded to os 4 yesterday and she's still smooth runnin.
I would think the radio in the hero is suspect, and that a firmware plus radio software upgrade would probably do the trick.
i'm thinking of selling the Hero, any takers, its unlocked.