Well, the thing they didn't say in the article is that height matters. For a 7 foot guy with an additional 3 foot reach (like Shaq) the underhand shot makes a huge difference in terms of the angle the ball approaches the basket. For a 6 foot guy with a 2 foot reach, the benefit of this shooting style is much smaller.

I think this is more a case of certain things being trendy for other reasons and ignoring success rates because until recently it was difficult to quantify one method as better than another.

It boggles my mind to imagine how much more awesome sports could be as technology improves and optimal styles develop.

Another reason not to used the underhand is that it can only be used on the foul line. (Can you imagine an easier shot to defend!)

When a high-level basketball player might shoot 50,000 shots in an off season why would they split time between two techniques? (Especially when the granny-method isn't fundamentally better when it comes to bio-mechanics)