I agree with that assessment, but there's no restriction in purchasing from Expedia et al, cancelling within 24 hours and having an itin to show. If making the transit BKK-DMK there's lots of reasons one wouldn't be able to check in/have a BP to show (international flight, CC check at counter etc) and would need to rely upon a printed itin instead.

If heading DMK-BKK there's also the possibility of an award booking subsequently cancelled, an option probably not available in the reverse direction.