I recently bought three packets of home brand pasta. All listed their only ingredient as "100% Durum wheat Semolina" but the stated calorie content for the fnal cooked product varied by almost 50% between the penne and macaroni and the spaghetti.

(In response to some comments in the answers section: Australian packaging laws requrie this information and require the figures to be based on a standard 100 gram serving. Therefore I suspect te difference is real and as the first asnwer says that it is probably based on the different rates of water absorption caused by the differing gemoetries of the different pasta products.)