Your default url to your account profile is what Steam gives you when you first register. What most of these people have done is go into thier profile settings and customized their URL to include their profile name. Nothing earth shattering, the only reason I've posted the info I did is that Steam lets players change their display name to just about anything, and in the soon to be common MP games you won't neccesarily know the real name of that person unless they let you add them as friends and then you can look up their profiles and do a little translation. This is actually the biggest thing I dislike about Steam is the difficultly in identifying players at times.( I can live with DLC and DRM)
At Civplayers we plan to engineer a mod after release that verifies players identity but hooking directly into the Steam API and using the Steam 64 bit ID that the API gives us to verify a player is who they say they are. And cross referencing this to the CivPlayers player database.
For anyone interested the Steam API does do quit a bit for programmers.
http://developer.valvesoftware.com/wiki/Steam_browser_protocol
CS