I dont know if its common in the anywhere else but in my town here in germany the stealing of bike-PARTS has become very popular. I guess the owners of high-value bikes use better locks, that are actually hard to break ( like those: http://ebay.muskelkater-sport.de/fahrrad/schloesser/bordo-gr... ). But for Parts the risk is even lower and a good break or light system can yield a few bucks.

I personally use a cheap ( 50€ ) used bike as a daily driver, in combination with a 30€ lock, there will mostly be an easier/better target for the thief and if it ever gets stolen, its just 50 (80) bucks and not 1000€.