It may not be "common" but it certainly happens, and as mentioned above, has mostly to do with the quality of cables/housing involved. After a couple of years of owning my bike and only occasional cable lubricating, my rear cable broke at mile 51 of the Palm Springs century. Bummer. It broke at the same place as yours, right where the cable end wraps and unwraps around the barrel in the shifter. This is normal use, and a high quality cable should be able to handle this for over a year, and usually over 2 years. You can visually check this 'weak point' by pulling the brake lever back and shifting through the gears while watching inside the shifter. If any strands of the cable are broken, you'll be able to see it long before the whole thing reaches it's breaking point (at least with my ultegra levers, not sure if the sora levers allow the same visual access to the cable or not).

Many people replace brake and shift cables every year, whether they need it or not. If you're in a specifically bad climate and your bike is typically "rode hard and put away wet" then you'll have to adjust your maintenance schedule to accommodate.

-Jeremy