I purchased the Commuter Case in Dec of 2012 and I'm already in the process of replacing it for the 2nd time. Both times, the plastic on the bottom of the case cracked. I am not hard on my phone. Sure I've dropped it a few times, but nothing that should have cracked the plastic.
The plastic is flimsy. Not very solid. Have read many reviews that say much the same thing - many having to be replace. You would think that Otterbox would want to replace flimsy cases with something more durable instead of having to replace them over and over again. the difference in price is about $10. If you replace the case with the Defender - you will be saving money in the long run.