teacupでopen-uriの挙動がおかしい

ruby 
require 'open-uri'
ENV['HTTP_PROXY']=nil
ENV['http_proxy']=nil

url='http://8008.teacup.com/XXXXXX/bbs?M=ORM&CID=1253&BD=12&CH=5'
`wget -q -O- '#{url}'`.length   # => 10892
open(url).read.length           # => 0
open(url, 'User-Agent' => 'Mozilla/4.0 (compatible; MSIE 4.0; MSN 2.5; Windows 95)').read.length          # => 10870

url='http://www.rubyist.net/~rubikitch/'
`wget -q -O- '#{url}'`.length   # => 10879
open(url).read.length           # => 10879

なんでだろう？？

追記：やはりUser-Agentでブロックしていたのか。どうもありがとう＾＾