So, you would trust something named 'googleserver.com' but not something named '1e100.net'? What if someone malicious registered 'googleserver.com'? There's nothing stopping them from registering that or any number of other names that sound legitimate. If you really want to be sure you can trust it, you need to check further anyhow.

And 1e100.net is a lot shorter than googleserver.com, which can make a fairly significant bandwidth saving for pages which contain a lot of URLs. Have you ever noticed that Facebook used fbcdn.net and Yahoo uses yimg.com for their CDNs? There are several reasons for using separate domains for their CDNs (security, to ensure that cross domain policies apply, bandwidth, to ensure that you don't send cookies to something that will just be serving up static images), but using a separate domain does mean that your URLs are longer, which on a high traffic, highly optimized page, can be a fairly substantial portion of the page content.

Finding a good, short, and descriptive alternate domain can be hard. 1e100.net is really not much worse than yimg.com or fbcdn.net.