3 GB of traffic for nothing

About two years ago I gave a part of my webspace to a few people, mostly Clonkers, who did not have any and needed one. They got their own subdomain and FTP access. One of them hosted a phpBB based forum related to some browser game. The last activity therein was from early 2005, but the account still produced about 3GB of HTTP traffic each month and used 120 MB webspace, which is even more than I am currently using (if you do not count email). Today I finally had a look into the access log, and guess what:

ck@unununium ~ $ grep Googlebot access_log_2006-09-19 | wc -l
2763
ck@unununium ~ $ wc -l access_log_2006-09-19
2770 access_log_2006-09-19

The remaining seven entries were spammers that posted nonsense into said forum, but I am still wondering why the Googlebot performed (and, well, probably is still performing) 2700 requests a day to that site - the arbur.net main domain receives not even 10.

You might also wonder why I have so much webspace I am not using. In mid-2003, when I acquired it, only 200 MB have been provided (which I have exceeded in the meanwhile - mostly via email on the IMAP server) and since then, the tariff has been upgraded two times up to 1GB now and I do neither want to downgrade to a lower tariff because of PHP and IMAP being not provided, nor do I want to change the provider since I made really good experiences with the support.