They were given the freedom of the sky, regardless of the airway. I believe Georger mentions bypassing PDX on the west side. they were west of a majority of population. you would have to fly over the ocean to avoid any kind of collateral damage. they were right over Vancouver, Toledo etc. not just Portland. I'm not sold they were that worried about the plane exploding or they would have diverted completely away from population.
Such simple questions to Rat could resolve this. many have spoken with him and fail to clear this up.
As mentioned above, the crew could of plotted the course out in less than a few minutes if they flew as straight as you claim.
I don't believe they mixed up the fighter jets with 305 either as Eric has mentioned. the SAGE tags every plane that is in the sky, 305 was in the air first and tracked prior to the jets.