How often do you need to monitor your EC2 instance for failed physical disks or bad sticks of memory... never :)
Additionally, it depends on how much you outsource to your cloud hosting provider. Many people trust ELB to do the right thing. It is a pretty reasonable product, but having used keepalived + the default builtin LVS[2] that is in every distro kernel out there for more than 10 years, why trust Amazon to do it better? Why use Amazon Dynamodb when there is Riak[3] or Amazon Elastic Cache when groupcache[4] is so awesome?
Using cloud services == outsourcing some/all of the traditional sysadmin work. Many people who consider themselves devops people are smart developers with very little real sysadmin experience. Please don't fall into the trap of considering them exactly the same. It is an interesting hybrid role, but is distinctly different.
[1] http://en.wikipedia.org/wiki/OSI_model
Everything you are describing applies to VPS systems.
There are differences, but those have more to do with optimal use of resources, and in that aspect managing cloud systems is actually more complicated. At least the behavior of your own physical systems is consistent and predictable.
Besides touching physical machines, what is it you think a sysadmin for cloud systems doesn't do?