I probably shouldn't have used such a initiative word like "will". That said scaling out PaaS compared to scaling out IaaS, specifically on Azure, is almost guaranteed to be less expensive from an infrastructure standpoint. Less actual VM's to manage also translates into less overhead from maintenance activities.

At the very least it will be interesting to see if more people adopt the Azure Websites PaaS offering. I know that right now most people dip their toes into Azure with IaaS because its historically more comfortable for them.