Agreed, I had a hard time getting the behavior described. Googling for "orange verse tangerine" finally did it. Other things that don't make as much sense to be compared, such as "giraffe verse tangerine" only produce a suggestion of "Did you mean..." but still it searched for my original query.

Seems Google does this for things that are likely comparisons (e.g. oranges and tangerines), which seems reasonable.

I work on Synonyms at Google. We're constantly tweaking our algorithms. It's possible that at one point one tweak made us more aggressive with replacing "verse" with "vs", but then later another tweak made it less aggressive. :-)

Neato :)