I don't think this article is touching the real world needs much.
I have a two node VMware ESX cluster with 18 GB each and I am running a virtualized installation of Exchange 2007 serving 60 users with about 2GB of mailbox data each, and I only have ONE virtual Exchange server and TWO virtual DCs, plus ONE Virtual File Server and ONE virtual print server. All the space it takes is 4 Us of rack space and performance is excelent.
I don't quite agree with the suggestions in this blog post that you somehow need to partition your Exchange deployment into so many different role servers. I would only do that for an user base of over 500 users, and in that case I would never use virtualization.
So I think this article is WAYYYY off base. Just my opinion.