you'll find out that 74 B737-700BBJs and 11 B737-800BBJs were ordered so far.
Airbus, unfortunately, is a bit secretive about the ACJ orders - the only reference I could find was "more than 30 commitments", but neither on Airbus' main website, nor on the ACJ website was I able to find any info more precise than that.
BBJ seems to be popular amongst the rich and famous and private Corps.
The BBJ is much more of a true "business jet" than the A319CJ. It has much more engineering changes relative to its commercial counterpart to make it better suited for long-ranged flights and upmost comfort.
Problem is, these changes make a BBJ unsuited for conversion into a commercial 737NG. The A319CJ can be (relativly) easily converted into a commercial A319. That type of flexibility makes it popular with airlines (especially those who opperate the A319).
Since the BBJ and A319CJ are closely matched in most respects, I'd say the trend of government purchases comes down to pricing and politics.
I'm not sure the ACJ is easier to convert in commercial airliners than the BBJ but I'm maybe wrong. Don't you mix the A319LR and the ACJ?
I know Privatair use the A319LR (and not the ACJ) and BBJ for the all-business flights they operate to USA for LH but to be honest I don't really know the difference between the LR and the ACJ except the cabin configuration. Could someone explain the difference?