No sexual purity in marriage?

Apparently purity rings are all the rage in America (or "some" of the rage). Jonas Bros wear 'em and so does American Idol winner Jordin Sparks. You wear it to symbolise how you're going to stay "sexually pure" until marriage, which I think means, no sex before marriage. Which kinda implies that sex in marriage is impure, or that you can become sexually impure when you are married (presumably because of sex).

I'd like to think sexual purity CONTINUES into marriage i.e. that you stay emotionally, romantically, sexually faithful to your spouse and you do not defile the marriage bed. You don't turn to porn. You don't turn to Mills & Boon. You don't turn to other people for sexual satisfaction other than your spouse.

Let marriage be held in honor among all, and let the marriage bed be undefiled, for God will judge the sexually immoral and adulterous. (ESV)

Hebrews 13:4

And there's so much more to purity than just sexual purity. This is what Jesus had to say about purity:

And he called the people to him and said to them, “Hear and understand: 11 it is not what goes into the mouth that defiles a person, but what comes out of the mouth; this defiles a person.” Then the disciples came and said to him, “Do you know that the Pharisees were offended when they heard this saying?” He answered, “Every plant that my heavenly Father has not planted will be rooted up. Let them alone; they are blind guides. And if the blind lead the blind, both will fall into a pit.” But Peter said to him, “Explain the parable to us.” And he said, “Are you also still without understanding? Do you not see that whatever goes into the mouth passes into the stomach and is expelled? But what comes out of the mouth proceeds from the heart, and this defiles a person. For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false witness, slander. These are what defile a person. But to eat with unwashed hands does not defile anyone.” (ESV, Empasis mine)

Matthew 15:10-20

I don't want to make light of the rings. Maybe it works well in the American context? But it is lacking in so many ways.