Very good advice.

In the event of a fire on taxi or takeoff, the ground around the aircraft is likely to be saturated with jet fuel; in the event you had to walk through that, you would stand a much greater chance and significantly reduce burns to your feet if you are wearing shoes.

A really great read for regular flyers is Nine Minutes Twenty Seconds, which sets out the backstory of all the passengers on a doomed commuter flights; it reveals facts both in terms of psychological make-up and the clothes they chose to wear which all had a significant effect on whether they survived the crash or perished.

http://www.amazon.com/Nine-Minutes-T...dp/0609810162/

Apart from travelling with a companion and/or actually having a deep seated desire to survive (surprisingly many people just "give up" in such a situation and resign themselves to death) one of the main contributing factors to survival was the clothing they were wearing, and especially robust footwear.

Some had such sever burns to their feet that amputation was necessary.

So while it should not be compulsory, and should be couched in optional terms, it is very good advice indeed, and worth following.