De nada guys, but don't make more of it than it is ...
It can be a little confusing at times talking about the various models, production changes and parts revisions, etc.
It also depends on who you talk to, as well, I'd think (as in any manufacturing company). Not everything changed by the engineers, or the reasons for the changes, always filters its way down to the customer service/parts level.
If I were to make a guess (and that's all it is, mind you), I wouldn't be surprised if the change (redesign) of the 9/40 striker mentioned in your email just referred to the early change made to striker's foot, when extra material was made to allow for more striker spring compression. If I remember right, this change was made in the 9/40 models before the .45 models were being released, so it may have just been carried over to the .45 strikers from the beginning of their production. Dunno. Wasn't paying that close of attention.
I can say that the first M&P armorer manual I received had the early 9/40 striker pictured and we were told that the striker had been changed to add more material to the striker's foot for the reason given. The corresponding pictures in the next M&P armorer manual I received had the updated striker pictured.
Here's an image of the same pages from 2 different armorer manuals, the earlier one on the left (showing the early striker) and the more recent one on the right (showing the redesigned striker with more material added to the front of the foot).
Maybe if I do another class for the M&P pistol the next armorer manual will have a picture of the newest striker.
The suggestion for snap caps is still worth considering, though.
Strictly as a personal preference, I've always been a bit reluctant to do much dry-fire with striker design pistols, myself. It's one thing to dry-fire a pistol with a 'conventional' firing pin which has a tapered body. The tapered body/tip can easily slip through the hole in the breech face. When it comes to a striker-fired pistol, on the other hand, I've just never cared for the thought of a heavy striker head slamming into the rear of the breech face for a lot of dry-fire.