I strongly suspect this has something to do with usage caps. From what I've read, EPB's business class service has pretty severe usage based billing. If you even approach saturating a gig connection, you will chew through your allotment very quickly.
Residential service does not have usage caps right now, but EPB's TOS does allow them to start usage based billing at any time, and apparently without warning. (i.e. they can charge you as soon as they decide you are using too much bandwidth)
From the TOS: "EPB reserves the right in its sole discretion to enforce bandwidth allotments depending upon your level of usage and the level of Service(s) purchased. If you have exceeded the appropriate level of internet usage in any given month, EPB will notify you by phone or in writing. You agree to pay additional charges upon notice from EPB."