I think the only reason they use megaBIT instead of megaBYTE is because they can advertise a larger number for the connection speeds. My 20Mbps Qwest connection really boils down to 2.5MBps. Which seems more appealing right off the bat?
Networking folks always use bits and bits/second instead of bytes. As one of these strange networking guys, I always think in bits and have to think "multiply by 8" when I see bytes to get a frame of reference in bits.