EC2 Instances Always Boot to Runlevel 4

It appears that Amazon EC2 instances always boot to runlevel 4, no matter what runlevel you set as default in your /etc/inittab. I found a very old reference to this fact in forums (see here), which explains how it happens (XEN does it) but doesn’t explain why. And yes, by passing “4” as last argument to kernel “command line” (as you can see here) they can do it. I am just wondering why…