As it has never been changed since 2009 (the first year of the queue system...take that failbot of '08!!) you have been absolutely able to change the quantity of tickets at Checkout. The pull down menu has been and always will be a trap.
Once you are at the checkout screen, pay attention to the yellow box area with your cart, ticket quantity, etc info. Immediately below that is a "Change Quantities" option which you click on, are able to input the quantity you want and then an "Update" button. You must hit the update button for your cart to register the change. Once it does, there you have it.
The queue system has always been about
HOW QUICK you can
GET INTO the ticket queue,
NOT about how quick with how every many tickets you get into the queue you are. Is it the perfect system? Probably not, but if you want to argue about how effed up of a system it is and how patently unfair it is, I submit as evidence in support of my argument..... the 2008 Blizzcon ticket sale process:
http://wow.joystiq.com/2008/08/13/ho...ket-situation/.... It could've been this......every damn year.