I guess you missed the part of my article about auto-scaling and restarts. The Rails app from my day job takes several seconds to come up, causing queuing and slow performance for our users. There are work arounds (idle instances, warmup requests, rolling restarts), but I personally would rather just have it start fast.
And with JRebel, Play or Grails you have no startup time anyway. You just hot swap the code in the JVM.