And a quick explanation to hopefully make things a little clearer:
The items listed as Snacks in the official brochure (soda, water, ice cream novelty, box of popcorn, piece of fruit, etc) are items that are widely available all over WDW property. If a location serves any of those items, those have to be offered as a Snack option.
But, each individual location can also choose additional items to offer as a Snack item. And because there's such a wide and varying array of items, there's no way to include all of them in the brochure. That's why they put the white-and-purple DDP logo next to items that are Snacks. There's also a single line in the brochure that mentions looking for the logo to indicate "additional items available as snacks".
The "snack-like item under $4" is a good general rule, but it's not the end-all-be-all rule. I've seen instances where it doesn't necessarily make sense, but the $4 rule isn't followed. At one point, a basket of onion rings at Flame Tree BBQ could be had for a Snack credit, while a basket of fries could not, even though the fries were cheaper than the onion rings. And don't be surprised if things change. The only things that HAVE to be offered as a Snack are the items in the official brochure.
Lastly, I didn't follow the links provided, but if any of them refer to things like boxes of Entenman's donuts in the resort gift shops as a Snack, that info is outdated. Disney caught on to that little trick a few years ago and started enforcing the "single-serving" part of the Snack definition.
-Rob