If you want to you can delete a site.
When logged into the blogging service, visit the dashboard of the blog you want to delete.
Check first that you have a working email address in Settings->General
If you do not you will have to set a new email address and confirm that address by replying to a mail that will be automatically sent.
Got to Tools->Delete Site
Check the Box that says:
Click Delete My Site Permanently
You will receive an email and need to click the link in that mail to delete the site.