[Vautrin]

I don't know exactly what DAP does, but most of the download accelerators use more bandwith, by making multiple requests. For instance they start to download the file at two or more points (at the start, and half-way the file). Thereby limiting access to the download to other people. Most sites are not too fond of that, for various reasons, sometimes going so far as to even ban users who abuse the file-servers.

Duke can probably give you more specifics.