The key factor may be that basketball has a salary cap and baseball doesn't.
Look at Buffalo's likely sources of cash and corporate sponsorship, and also the massive start-up outlays for baseball (like funding a farm system) in addition to the franchise fee, before you even get to player salaries, and you get something behind the Kansas City Royals. It's not going to happen. Basketball has smaller capital requirements (franchise costs less, no farm system outlays, less front office, the facility -- HSBC -- is already there) AND a cap keeping all teams closer to each other, so it's more realistic even if it's still not going to happen.
In baseball, even if Oakland and Cincinnatti can win a few games they're not really perennial serious contenders like the Yankees and Boston and even St. Louis (every corporate dollar in that part of the country sponsors the Cards). In basketball, San Antonio can be a perennial champion and the Nets (who don't have nearly New York's money) can be pretenders.
Of course, the real bottom line is competence. Hence the Atlanta Braves (+) and New York Knicks (-).