DSMUnknown, it's only done to smooth the path. Studying head/intake porting, you quickly see that a smooth path is paramount to a slightly larger OR smaller diameter path.
Back to the 2g elbow. It is better because most intecooler piping comes out to the same diameter as the 2g elbow. Knowing the previous paragraph to be true, the 2g elbow yields a nasty lip when mated to a 1g throttlebody. So we port the elbow to match. That is all better than accepting a tiny diameter neck down when running a stock elbow and 2.5 inch intecooler piping . . .
Other than that, your soap box has washed
.