Having just read the post I disagree. The post clearly says that most current vendors place significant restrictions on the software and networking layers in their cloud. As someone who has used GoGrid, Rackspace and AWS I can concur with this position. You have a lot less control over your cloud servers than you do over say a dedicated server.

CloudSigma are an IaaS provider who presumably take a different approach.

Overall I think it is a valid point for them to make, especially as it seems that a lot of these restrictions are vendor created.