Shoutingwind,
I think it really depends on the type of person who would be willing to do something else to get a foot in the door if at first unsuccessful. By the way I lost the screenname ItsAllMagic ever since they decided to just show usernames.
keenas,
Relax man you haven't done anything wrong
I think you're basically right, a Commissioned Officer has greater overall responsibility, and is expected to lead. Which is why he/she gets the higher rank. There are also Non-Commissioned Officers (NCO's), which seem to form a bridge between the Officers and the Airmen. But I'm sure someone can explain this much better than me.
As for the medical....expect to bear all. The psych and defence interview are just answering basic questions so they can rate you for suitability. Don't get nervous about what you don't know, just do what you can then be confident about what you do know!
Cheers