I switched web hosts for 2 sites a while back. After the switches, I could swear the site's rankings were higher since I got a lot more visitors without doing anything else. Here is my rule - if your site's rankings are high, you need to have a strong reason to make the change; if your site's rankings aren't high, you really have nothing to lose, then go for a good web host. Keep in mind that search engines change their ways of ranking all the time. The Matt Cutts' piece was over 1 year old. In the SEO world, that's almost like enternity.