1. Actual track racers use aerospoked front wheel because aerodynamic drag is greater at the front wheel (a like 2% advantage can be had by going aero on the front) than it is at the rear wheel (the rear wheel is in the aerodynamic "shadow" of the seattube, you can only gain like 0.6% more efficiency back there). So, you gain the greatest aerodynamic benefit by using a aero front wheel. Using an aero rear wheel doesn't give that great a benefit, so some track racers have a more "standard" rear wheel so they don't have to run two "brick style" wheels.
2. Some messengers like to go wicked fast, and since they are on track bikes too, why not also run the same setup?
3. Hipsters see what the messengers are doing, even though they don't know why they are doing it, so they do it. They later try and figure out why they did it, and come up with crazy ideas like "Doood, I run an aerospoke 'cause I can lock it up real quik in the rear" STFU!
4. Barneys who are interested in becoming hipsters get caught up in the hype and bid up the Ebay for aerospokes, just because they don't want to miss out on the next BIG THING!