It looks like for your "55% support 'stay the course', 63% support 'Murtha's plan'" figures you just added together the "all" column's strongly support and support rows.

If this is indeed the case those numbers work out to exactly 53.8% for "stay the course" and 63.3% for "Murtha's plan".  While 63.3% would normally be rounded down to 63%, and 53.8% would be rounded up to 54%, that only gives you 54% for "stay the course" not 55%.

This may seem like minor nitpicking, but there's already enough other factors being fudged in favor of the republicans in little ways.  Normally any poll like this (if it even asked about Murtha's plan, would not describe it but would simply say "Murtha's plan" and trigger the knee jerk "must vote against" reflex among many.  As it stands, I suspect that Republican support for the war would be far lower if they didn't see it as a Republican thing.

Granted, democrats are afflicted by partisan blindness too.  It seems to me though that democrats more often vote against DEmocratic talking points then Republicans do against republican talking points, for whatever reason.