"Manufactured collectible" is a term that describes something made on purpose to sell for more money than usual, to declare itself a "collector's item", or to be a (ratio) incentive to generate more orders.
Newsstand books didn't do any of those things.
Sure, that makes sense. But that's your definition. Personally I don't like the term, was just joking around. Everything is manufactured and everything is collectible to someone, so it has no real meaning.
It's not just my definition.
"The terms special edition, limited edition and variants such as deluxe edition and collector’s edition fall under the category of manufactured collectibles, since they are used as marketing incentives for various kinds of products" -link (not my site)
No, it's not just yours. I see it thrown around on here from time to time. Actually, if you search for that term, CGC comes up pretty often in the early results.