Why Congress is pushing a public "option"

Because they won't have to be covered by it. It would, after all, be a pretty big step down from what they have:

A choice of 10 healthcare plans that provide access to a national network of doctors, as well as several HMOs that serve each member's home state. By contrast, 85% of private companies offering health coverage provide their employees one type of plan -- take it or leave it.

Lawmakers also get special treatment at Washington's federal medical facilities and, for a few hundred dollars a month, access to their own pharmacy and doctors, nurses and medical technicians standing by in an office conveniently located between the House and Senate chambers…
Why can't everyone enjoy the same benefits as members of Congress? The answer: The country probably couldn't afford it ...

The plan most favored by federal workers is Blue Cross Blue Shield, which covers a family for about $1,030 a month. Taxpayers kick in $700, and employees pay the rest. Seeing a doctor costs $20. Generic prescriptions cost $10. Immunizations are free. There is no coverage limit...

There is no such thing as a preexisting condition...

No word on whether Nancy Pelosi said "Let them eat cake!" literally or only figuratively.