Question to the SharePoint community..am I missing something in the docs?

If you have ever taken advantage of the great APPTIX 30 day try out offer you'll notice that they have some very good business processes around new clients creating SharePoint sites!

One thing I like is the way they do their site naming conventions. Currently like many hosters we add new sites into collections so for example

www.abc.com/sites/<new site>

but appitix would have that as

<new site>.sharepoint.apptix.net

when you go to the site you created it is indeed the URL.

now with them a different site , ex: old-site.sharepoint.apptix.net

will also have the same physical IP address.

So my question is: is this the result of host Headers? How do they do this?
is it out of the box IIS/SharePoint functionality?

here is their signup page https://stssignup.apptix.net/signup1.aspx