This is a bug with Safari in iOS 7. It appears that the favorites icon gets confused by redirection and does not honor the icon on the specific favorite page.
To replicate...
* Click on the + sign to get a new tab.
* Click on the Google icon.
* Search for Apple.
* Click on the first link to go to the Apple website.
* Click on the + sign to get another tab.
* Note that Google now has the Apple logo.
When you click on the Apple link from the Google search results page, you do not go directly to Apple's site. You first pass through something like this (truncated for readability)...
https://www.google.com/url?q=apple&url=http%3A%2F%2Fwww.apple.com%2F
This page does a redirect to the final destination.
What I suspect happens is Safari thinks it is going to a Google site when it hits the redirect page, then follows the redirect to get the icon.
This happens with Yahoo as well, but not so drastically. After a search on Yahoo, the Yahoo icon will be replaced by the Yahoo Search icon. Visiting Yahoo again will change the icon back to the Yahoo icon.
This kind of redirection pattern is pretty standard since it helps with analytics.