I probably own 15 Nitecore lights and about the same number of lights from Fenix. I don't purchase the entry level lights, so I think that the manufacturers take more care in building a $100 light than a $40 light. I'm not making excuses for the manufacturers, but the build process on low cost lights isn't conductive to the highest of quality.
The only light that I have that failed was a Surefire M952TVN, but that was my fault when the hand guard that it was mounted to went splat onto the concrete.
I think the majority of problems with any of the name branded lights is cold solder joints. One low level drop is usually enough to break the connection, and it don't work anymore.