site:sitename.com vs. site: sitename.com

Google Sitemaps provides an easly link to see your Index stats.

I have noticed that "site:sitename.com" provides different results in
Google as opposed to "site: sitename.com"

the difference is the space.

try, for instance

site:gizmodo.com (292k results) vs site: gizmodo.com (492k results)

or, in my case

site:mocoblog.com (13k results) vs site: mocoblog.com (598 results)

why and how?

Amar