New Bloke, I agree that your instructor maybe dealt with you a little brusquely, but you need to look at your own attitude too.
Even as a PPL you need to be disciplined and professional but also be flexible and always willing to learn.
Many things change and evolve through the years and in the main this is an improvement.
Accidents happen and procedures and "best practice" is changed to avoid a repeat.
Just because you have been flying for a number of years and have 400 hours (not that many for someone who has been flying a number of years) does not mean what you are doing is the best or safest way to do it.
I believe the reason for not cleaning up on the runway is to avoid accidentally moving the wrong lever (for example moving the gear lever up rather than the flaps lever in a retractable), that sort of thing. To me, good practice says turn off the runway and stop, clean up, contact ground frequency if appropriate or ask the tower for taxi instructions. This is good practice and safe.
I am always open to ideas, I think I can always learn something from an instructor I haven't flown with before. If it is different from what I have done before I need to consider it and understand the reason it is a better way to do it. I would happily discuss it with the instructor. I do not believe in something for the sake of it, other than standardisation amongst instructors, that sort of thing.
So be open minded yourself, be flexible and keep up to date with the latest thinking.