Erin,
I think that some of the sites you are going to are using correct specs, but they are giving the air speed of the blower with out any tubing to direct your airflow. Measuring speed without restriction will give you a higher number, but it isn't too helpful.
Here is the airspeed and CFM taken at the end of the tube attachment:
Air Speed (mph) 251
Volume of Air (CFM) 494
Now that I have cleared this up for you, I wish you the best in your fall clearing!