you can find the whole newsletter here:
http://www.cavecreek.net/newsletter
it kindda took me by surprise. i remember, i was hosted at Cavecreek when i first started in this business, few years back, and they used to be big FreeBSD supporters.
maybe they have strong reasons to suggest a move from FreeBSD to Linux.
honestly, i don't think Linux is any securer. I swithched to FreeBSD 2 years ago when my Linux box got hacked through DNS.