Is there much of a difference between magazines received by subscription and those sold at news/magazine stands?
You are correct about the inserts. In the newsstand issues there often are invitations to subscribe to the magazine and occasionally a promotional world map, while in the subscription issues there are things like the Society's wine club.
As to the issues themselves, the articles and supplements are (as far as I know) are identical.
As for the covers, it varies. Some are identical except for the Barcode in the lower left or right corner. Some have minor variations to the headlines or other verbiage, while some major formatting changes. A few have different covers altogether.
See my post on Cover Variants here. Most of the newsstand/subscription variant are toward the bottom of the post.
I hope this answers your question.
Yours in collecting,
Thanks again, Tom! I'm finding this extremely interesting.
I'll probably have more questions for you!