in the sample that you sent me the wireApplication() method was never called, so the application context was never created and stuff.
When I added this to the s:Application tag:
the autowiring worked perfectly.
minWidth="1024" minHeight="768" xmlns:ns1="*"
I hope that solves your problem, but maybe you just forgot it in the sample app, let me know how you fare...
P.S. I noticed in Flex 4 apps that using the applicationComplete event is the safest moment to create the application context, when using creationComplete not everything that is on the stage by default will get wired properly. In Flex 3 this was't a problem, we'll look into this.