The whole tradeshow thing is something of a racket--speaking as someone who has been involved with tech tradeshows in various contexts for more years than I care to admit. As you suggest, there are lots of cities and lots of convention centers, at least until you get above a certain size in which case your options drop dramatically. But I suspect that moving most tech conferences to $RANDOM_MIDWEST_CITY wouldn't be a popular choice among potential attendees. (Not that I'm personally a particular fan of certain popular venues like Vegas but many are.)