I've been told the SAME thing and I completely agree with downshifting and disagree with braking...
1) your manual suggests it and
2) that's what your tranny is made for. You gotta figure when you pound on that gas pedal, you're putting a lot of stress on your tranny anyways, what difference is there going the opposite way? Your engine only revs so much and your tranny was built to handle your engine speeds. Now that's not to say you want to slam it into 2nd gear at freeway speeds - just be smart about it and it'll be fine. I was taught that you slow down using your tranny and I've been doing it for years and I've never had ANY problems with my trannies on any of my cars.
Just my 2 cents...