pakistani applications used to be processed at the local VO in pakistan. however, london VO took over from them in 2013 and is now responsible for processing all pakistani applications for permanent residence. london VO went through a bit of a learning curve when they initially started processing pakistani apps, almost as if they were trying to grasp a better understanding of pakistani culture and all of its nuances. this tells me that they can process applications at any visa office around the world, but as you said, it is not optimal since this would require the CIC to train all of its visa officers to understand the specifics of every culture in existence. the end result? the greater the volume of applicants from a certain country, the longer they're made to wait. unfortunate, but understandable.
...but does that mean they are justified in keeping spouses physically separated while their applications are processed?
John McCallum A.K.A. Emperor Palpatine once said that they cannot turn a battleship on a dime, but we're not exactly asking them to turn a battleship on a dime; we understand that it's going to take time for them to speed up the processing of spousal apps. what we're really after is the privilege of being able to stay together with our spouses/partners while the CIC processes their applications. the americans have something similar to a spousal TRV, so why can't we have that as well?