To bust the conspiracy theory: CSR and TSR folks have no ability to 'bump your speed' up while on a call with you. What you tested was what was available during your call.
Cable uses DOCSIS which is a Shared architecture. It is a much bigger pipe than DSL (and getting bigger and bigger all the time!) but access uses a contention mechanism.
This awesome article by Ars Technica describes DOCSIS and how it works pretty well for the average human: »arstechnica.com/business/2011/05···-access/