Note that they consider it a mid-size vehicle instead of a compact. These specs still don't show gas milage, but the horse power ratings are there as are the vehicle dimensions.
"The size class for cars is determined by measuring the interior volume ....
Compact Between 100 and 109 cubic feet of passenger and luggage volume
Mid-Size Between 110 and 119 cubic feet of passenger and luggage volume"
According to the document you listed,
the current generation Prius has a
total interior volume of 100.4 cu. in.,
while the new 2004 Prius has a total
interior volume of 110 cu. in.