IMHO, SDSL is a commercial service, and having high upload bandwidth allows servers at that site.
I have SDSL at home at is marketed as ADSL from Speakeasy. Servers are OK, but if I use all my uplink bandwidth on a consistent basis, I will be converted to commercial service. I did not know it was SDSL until i did the RTFM trick on my Efficient 5250, however.
JMHO
Doug