Hey Jake,
Thanks for the question. While it's true that many retailers ask for delivery information before presenting the total cost, many others ask for billing+shipping information before displaying the total cost. These sites will then land the user on a "review order" page where they present the total cost and give the user a chance to cancel their order. Target.com is an example of a site that does this.
We're modeling our best practices after the latter flow, because we think that reducing the number of steps in a checkout flow--by having the user submit their billing+shipping information in one shot--provides the best experience. We're recommending site authors give users a chance to review (and potentially cancel) their order before processing the payment.
Alternatively, a site author can use requestAutocomplete to ask for only shipping information, present the total cost to the user, and then use requestAutocomplete to ask for billing information. In our opinion this experience is not as streamlined as what I described above, but if merchants think that this is important to their checkout flow, they can still use requestAutocomplete to offer their users a checkout experience with no typing and only a few clicks.