Actually, the members of congress do have Obamacare. They purchase their insurance through the DC Insurance exchange. 72% of the premium is subsidized by the federal government though.
When you are paid by the government, what's the practical difference between what you pay from you salary (which you receive from the government) and what the government "subsidizes?" It's all just part of your salary package. That's true with other employers too, actually, regarding the employer-paid portion of premiums.