I totally agree - and my reaction to the whole "it is just sleight of hand and/or fixed through trickery" theories may explain some of my apparent "cynic" type posting above.
What Derren does is perfectly understood and agreed theoretic (and via other means practical) understanding of psychological techniques. There is no doubt that these things can work and do work.
He openly acknowledges that it is through (mainly) NLP and, to a lesser extent, hypnosis, that he achieves what he does.
For me, the fact the he can use these techniques to such impressive and devastating levels are the genius of what he does.
We can all read the techniques - they exist. Some people have a natural attribute to perform these techniques - some people work hard and are able to perform these techniques. Others are just greats showmen.
Derren Brown combines the three - the secret to his work is pure hard work and an ability to use these techniques more effectively than others (just as some people could spend their lives training to run the 100m and still not be able to run sub-11 secs, Derren has a mind that enables him to utilise these techniques like a 9.8sec runner).
Add to this his showmanship - and you have a compelling combination.
To explain his performance by conventional trickery just misses the point - IMHO.
On that point, were Derren's performances to be revealed as mechanical trickery - I would be a very upset and disappointed person.