I can't disagree more, but that's only true in proper context. Let me explain. If you have multiple sites on the same topic, or even different topics, that you want to cross link you will need either dedicated IP addresses for them or host them at different hosts to avoid any possible link farming and negative influence on search engines. Since dedicated IPs are expensive to have, especially if you own a lot of sites, it is much cheaper to host with multiple companies. I have hosting accounts with 3 different companies and so far my strategy works like a charm.