I would be really surprised if the host affected Google rankings -- is there perhaps something else that is common among these sites? Perhaps they are all recently registered domains? (I'm struggling with some recently regestered domains and have found
SEO much easier with established sites, even when they were sitting dormant.) I suggest this because I know GoDaddy is also a registrar.....
I would be quite interested if this is the case. We have been recommending GoDaddy to our clients who we are kicking off of our server. We had to get out of the hosting business. We were doing it for convenience and as a courtesy and were not making money at it. We'd rather be designing websites than troubleshooting email problems. It gets ugly and frustrating.