But they aren't hosting your site. At least, I didn't see anything about offering webspace on the page.
You can have your email server MX record point to a different server than your DNS record for your site. Hosting email can be a pain when it comes to filtering, spam, viruses and users who don't want to clean out their account.
There is an option to host pages as well, but I don't think they support dynamic content of any type.
When you are hosting multiple accounts for a guild, or small company, you don't just tack them on to your ISP account.