I'll answer that by answering the OP's (b) and (c) question:
How much weight should I attribute to it? None. It may mean that you've recruited a higher rating player from the D3 ranks, but its really about potential and his rating in categories that are important to your offense and defense. I've recruited 480 rated D3 guys with 80 durability and gotten this email. That means I recruited a guy with 400 rating for all the other categories. In the end, not that great a player.
How many guys get this email? I have no idea. But I can say, the guys I have recruited where I got this email, made no difference at all if they ended up AA or not.
To answer your question, How can it be dressing if its different? I believe it to be true that you will get this message for higher rated players. But see my answer above. In the end, it means nothing compared to where his rating is allocated and compared to your team needs. It makes no difference on his actual chances to be an all american. Therefore, IMHO, its window dressing.