As a microlight CFI - ie one who has a few instructors he is responsible for - and a Flight Examiner (so ground and reval examiner too), he is my tuppence worth.
First, the NPPL Micro reval is a little different from some in that it is 60 minutes total time with an instructor - so could be three 20 min flights. In JAR land, I believe it is a flight of a minimum of 60 minutes.
However, little things like this is not really the bread and butter of being a good flying instructor. Knowing today's rules doesn't mean you know tomorrow's. As Genghis has show ;-)
There has, indeed, been a great deal of convergance over the years with air law - flights over built-up areas come to mind.
I think the best thing as an instructor is to be a good instructor! And part of that is being able to assimilate and communicate information. So picking up on differences shouldn't be too much hassle.
Flying C42s - I have found - has been a doddle for Cessna instructors. A few differences - mass, power ratios and inertia being some. But the students make the same mistakes.
Weightshift to three-axis, or vice versa, is more "fun" - but many microlight instructors jump in and out of the different types all day.
Never found a problem driving my car home because it doesn't have a stick - or a control bar - or a tiller like my boat had!