tedster - 8:26 pm on Mar 26, 2012 (gmt 0)
Zero results is your answer - no one is linking to the URL for your RSS feed. When you add the space, you are using a regular query that includes the word [link]
There is all kinds of data available from third party sources, some of which Google may well access. Sites like Alexa, Compete, SpyFu and so on - even with all their inaccuracies - still provide a decent guesstimate of all types of user engagement. And a lot of what Google is using, IMO, is this kind of secondary indicator of what they are calling "quality".