Routerstats and DSLstats must be using the same commands to gather the data, and in neither case do they receive any, although the telnet login is successful.
I've had a sudden thought - are you running Routerstats and DSLstats at the same time? If so, it could possibly be the problem.
Otherwise, could you manually log into the router by telnet, then type:
xdsl info expand=enabled
(exactly like that) then see what the result is. From what you've said, I would expect there to be no output, but there may be an error message.