Hmm. I have to think about that a bit. On the face of it, EC2 and colocation require completely different skill sets, and those skill sets don't overlap very much.
Being a good Linux sysadmin might be fundamentally harder than being a good EC2 sysadmin; I'm not honestly familiar enough with EC2 to know.
I would point out though that Amazon has a vested interest in making EC2 less hard, so I would be surprised if the general opinion was that EC2 administration was just as hard as Linux administration.
EC2 instances are running some OS, whether it's Linux or BSD or Windows or whatever. The only thing that doesn't overlap is hardware tuning and maintenance, and even there you should be using the same tools to figure out if you've got a hardware bottleneck on your EC2 instance as you'd use to evaluate performance on a standalone box.
Being a good Linux sysadmin might be fundamentally harder than being a good EC2 sysadmin; I'm not honestly familiar enough with EC2 to know.
I would point out though that Amazon has a vested interest in making EC2 less hard, so I would be surprised if the general opinion was that EC2 administration was just as hard as Linux administration.