I can't see any reason why DSLStats couldn't use the HTTP interface
To do so would mean an entirely different approach and probably encroaching in an area the John already covers with routerstats.
DSLstats uses telnet and the router's CLI which provides far more information about the line stats.
Its an entirely different way of doing things, Im trying to think of a simple way of putting it, but a similar difference could be described as how you need a web-browser such as Firefox to fetch and interpret information using the http protocol from a server or you need an ftp client such as Filezilla to fetch or put files from/on a server using the ftp protocol. The webgui GUI uses http whilst the CLI uses telnet. Think of Johns program as the former, Erics is the latter. So it would be a major overhaul to make DSLstats perform like routerstats.