My first association was with the character from the UK children's TV show Rainbow: http://en.wikipedia.org/wiki/Zippy_(Rainbow)

I doubt it's a trademark issue, as trademarks tend to be usage-specific. (e.g. Apple Computer vs. Apple Music) It's probably just a matter of Google feeling there are too many different things already associated with the name 'Zippy.'

(I also now have the "Rainbow" theme tune stuck in my head.)