Not even that. The arcs represents the possible positions of the aircraft at the time of the last ping. This seems to be mostly based on the measured distance of the plane from the satellite and the limits on the altitude of the aircraft. This ought to yield a full circle. Consideration of satellite coverage eliminates parts of the circle, and other parts have been eliminated by consideration of the range and possible speed of the aircraft.
Yes I think you might be correct. You must have copied my post when it was still a draft before I edited it.
I thought that they had multiple pings but your suggestion that they only mapped the final ping actually fits better. What are the odds that multiple pings would have exactly the same strength as shown in the arc (unless the aircraft was stationary by that point)?
EDIT (3-16-2014): The arcs are possible locations of the last ping from one satellite. This fact is being reported very well by some broadcasters (so well you would wonder why there was ever a question) but still being called a "flight path" by other broadcasters. The "flight path" broadcasters are doing it wrong. Obviously I got my original information from the "flight path" sources, hence my confusion.