@viybz
yes and no..
these days you can pretty much wear whatever..but its obvious when you go to a super formal event, and you don't have the stripe down the pants, or the sheen on the lapels..etc. especially in photos.
i think its important to have a distinguishable difference between a "simple suit," and a "i spent extra time to make sure this outfit is perfect for this classy event i've been invited to,"
for weddings i don't think its a big deal to do either one, but the tux at a formal white tie (the most formal) event is important.