And how many of those are significantly different between the two options? Either way, you still need one or more sysadmins, you still need a backup setup. Sure, there are extra maintenance costs associated with owning the hardware, but what portion of maintaining a server infrastructure is tied up specifically in that, and how does it scale relative to the size of the cluster?

In my experience of managing a team of 10+ admins, less than 5% of their time was spent dealing with physical hardware and that includes installation and repair.

Today's equipment is very reliable.

But the most expensive resource is human resource, specially expert ones.