You hit the nail on the head !!!!!  The rush of boarding and the blocking of aisles is 90% about securing your overhead luggage space. 

The big point of difference between Virgin and Jetstar for me is the baggage allowance and how they total it.  Virgine is ONE piece up to 23kg and Jetstar is any number of bags that add up to the total weight of your allowance.  I got caught with Virgin - 2 pieces with total weight 16kg...