there seem to be a lot of misconceptions here smooth...
the commission isn't composed of serving congressmen. in fact, only four of the ten on the commission ever served in congress (hamilton, kerry, roemer and gorton i believe).
i do not have a low opinion of the offices of representatives or senators, but my reverence for that is far outstripped by the office of the Presidency. i'll tell you why i have a higher respect for the President, because he is the only person elected on a national level (not to mention all the power he weilds as the country's chief executive and diplomat). i would argue that the President is most vulnerable (although not most accesible) to those he represents because every action of his is scrutinized and publicized to a degree that isn't applied to congressmen on a daily basis (nor should it be). also, as we all know... the president is elected by votes from the electoral college. many state elections are held on the same principles (i.e. not necessarily won by larger portion of the popular vote)
newsflash: none of the commission members are elected officials however distinguished they all may be... let's be upfront with that. most are lawyers and university administrators whose credentials qualified them to be appointed to this position.
here is a good look at the commission's roster:
http://www.9-11commission.gov/about/bios.htm
you're crazy if you think the president isn't above members of congress, there just isn't an argument to be made there. he may not be above congress as a whole (every single representative and senator combined), but he is certainly WAY above any single individual or segmented group. our government is designed so that the branches are in equal footing. the president, by and large, IS the executive branch... a congressman is way less than 1% of the legislature.
in situations like this, the President IS NOT answerable to a commission unless the commission gets a subpoena for information the executive branch holds. the President chose to meet with the commission out of cooperation, not because he was legally compelled to do so (as in your analogy of judges).
a lot of this is in a civics 101 textbook.