I have quite a few friends who choose not to vote based on their religious beliefs, but the reasoning is quite different than what you list for Jehovah's Witnesses. They derive their beliefs roughly from the anabaptist tradition (not to be confused with baptist), which also spawned what are now known as the Amish and Mennonite communities.

At its most basic, their decision not to vote is derived from a commitment to pacifism. In this case, pacifism is a belief that there is no such thing as redemptive violence---all violence, even taken in self defense, is believed to be a sin. As such, there is no such thing as a "just war." The claim, which I think is a reasonable one, is that despite any rhetorical promises of democratic freedom, no nation-state will allow a pacifist to be elected to its highest political offices, as it is anathema to the state's security. The matter of conscience comes down to whether or not you believe you can participate in a system without endorsing it. Most anabaptists think you can't, so by participating in the election, you are endorsing a system that relies on violence for its own maintenance. Thus, many pacifists choose not to participate in political elections.

I'm not attempting to defend the belief here, simply explain it. If you want a more detailed treatment, you could read the recently published "Electing Not to Vote" from Wipf&Stock Publishers