I'd say Amazon Prime is a different animal entirely, but Prime Now and all those other businesses are all focused on building a new "last-mile" delivery model (with some nuances around point-to-point delivery vs warehouse fulfillment)
If you can deliver one thing at cost, delivering a second thing to the same person is gravy. I think a lot of these companies are converting on the same location because a $5 delivery fee for a package will mean the $4.99 delivery fee for lunch is profit. They're trying to all capture a second delivery market.
I dunno, I feel like this is a mash-up between GrubHub and Amazon.
Postmates is cool because they have the logistics to get you your food but they ALSO have the integration with the store menu and ordering system (maybe in the future, real time inventory).
It's more like Instacart, but the grocery is the restaurant, the shoppers are the food preparers, and the delivery people use bikes or walk instead of a car (important due to lower fixed costs for the delivery people).