They require a User-Agent header:

Code:
on *:sockopen:DotaBuff: {
  echo -ag DotaBuff Sockopen
  if ($sockerr) echo -ag $sockerr open 
  sockwrite -n $sockname GET /players/35434359 HTTP/1.0
  sockwrite -n $sockname Host: dotabuff.com
  sockwrite -n $sockname User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.5 Safari/537.36
  sockwrite -n $sockname Connection: close
  sockwrite -n $sockname
}