It appears to be an issue with recent iPhone models based on some Internet searches I performed.
My iPhone 5 is having power button issues too. It is not jammed and has not been exposed to water or dirt and I have had it in an Otter Box beginning the day I received it from Verizon.
The issue I am experiencing used to be intermittent and at first I thought it was just me. Then the right side of the power button stopped working, but the left side continued to work fine. Starting a couple days ago, the left side started having issues and now it is very difficult to get the power button to respond at all.