Ok, it looks like a little DC electrical lesson is in order.....
I only have a basic 2 year electronics degree (from many many many years ago so I have forgotten the majority of it) so I don't claim to be anywhere near someone that can speak with any authority on the subject, so I fully expect others to chime in and correct me where needed.
When the jumper is left in place on a Skytech starter to avoid using a second activation wire routed to the solenoid, the power input side of the solenoid is connected directly to the power input of the starter motor.
When the start circuit is activated, the starter motor and the solenoid are both fed power via that one wire, the motor turns and the solenoid pushes the drive gear fwd to engage the ring gear of the engine making the engine turn.
When the start circuit is deactivated, power is removed from the starter motor and the solenoid, but the solenoid is still electrically connected to the +V input side of the motor.
Why does this matter? Because at this point the starter motor has now converted to being a DC generator. It is still spinning (driven by the now started engine) and with its power input connected to the solenoid, the
Reverse EMF produced by the spinning motor works against the collapsing field of the solenoid coil. This keeps the solenoid/starter drive engaged for longer than it would be if the power was interrupted instantly as happens when a separate activation wire is used.
This delay can be quite noticeable in some instances, and as I mentioned previously can cause an annoying noise that has the sound of an unhappy mechanical device. Particularly in instances where the engine goes to a rather high RPM immediately after starting (higher the RPM, the stronger the EMF that is produced).
As I said in my first post, Skytech has always said this was not detrimental to the life of the starter (do we know that for sure?), and that doing it the Van's way was optional.
I find it interesting that they now have this diagram on their web site and they say they don't know why Van's does it this way.... Well as far as I am aware, no one at Skytech has ever called to ask!
BTW, this wiring scheme was not my idea. It was conceived by the late Bill Bennedict... former general manager of Van's Aircraft (and Electrical Engineer)
BTW X2, I recommend caution in arbitrarily changing to the NL starter. If you are using the Van's supplied fwd facing induction system (affectionately referred to as the snorkel), an NL starter motor wont fit.
Bottom line? It is experimental... you can do what you want. We have been doing it this way for 18+ years and we get very good life out of our starter motors (and our normal mode of operation results in probably way more engine starts per hour than the average user).