Just did a test:

$ HEAD http://en.wikipedia.org/wiki/Hotel | head -1
403 Forbidden
$ HEAD http://www.perlmonks.org | head -1
200 OK
$ HEAD "http://search.yahoo.com/search?p=hotel&fr=yfp-t-103&toggle=1&c
+op=mss&ei=UTF-8?" | head -1
200 OK
$
[download]

HEAD is a perl skript provided by libwww-perl.

While wget (perl independent package) results in:

$ wget -S -O /dev/null  http://en.wikipedia.org/wiki/Hotel 2>&1 | head
+ -5 | tail -1
  HTTP/1.0 200 OK
[download]

So it looks like they don't like perl (or whatever data is sent by HEAD) at wikipedia...