"I started questioning all those who say you should optimise your code with assembly. Maybe they dont trust or know the great new c compilers like keil."

There are some people who think that just writing in assembler per se gives you good, tight, fast, efficient, compact code.
This is, of course, nonsense - assembler does allow you to get the most out of your processor, but it certainly doesn't stop you from writing rubbish!

Yes, a good modern optimising 'C' compiler can give you very good code - but, for embedded work, you still need to understand the underlying architecture to get the best from it.