i couldnt disagree with you more... so according to you lets just throw out physics...
in fact go here:
http://www.wheelweights.net/
look up same make of wheels and look up different sizes and their weights:
example:
Volk TE37 15x8 11.5lbs
Volk TE37 17x8 16.3lbs
Racing Hart CP-035 15x7.5 9.7lbs
Racing Hart CP-035 17x7.5 13lbs
OZ Superleggera 15x7 11.5lbs
OZ Superleggera 17x7 15.2lbs
you might be thinking that its only a couple of pounds of difference (5-7lbs) wont make a huge difference right?? wrong...
simple as that... you have to realize unsprung weight is alot different compared to sprung weight.
im not going to get into that but search and you'll find info... google is your friend.
also look into moment of inertia while you're at it... basically what dc2GS-R said in his posts.