I am frankly cynical about trusting such figures with much confidence. However there are some variables even when the pasta is allegedly pure semolina of the same variety.
The most obvious would be the water content of the final product. Not all recipes use pasta equally al dente. Pasta boiled soft will contained more water than pasta al dente. Secondly, thin pasta, such as spaghetti, not to mention vermicelli, becomes saturated with water much faster than thick pasta.
That is the most obvious probable cause, I should imagine.
