I don't completely agree with you.
Who Says You Can't Go Home and the duet version also, they've both been releases, one to US country radio and the other to US non-country and non-rock radio stations, they both aren't available for sale, just like IWTBL, and aren't released in Europe (and other places too, except US). The only difference is they promote WSYCGHA and they filmed a video. But why does this make it a single release and not IWTBL. All of them exist only as promotional singles in US.
I believe IWTBL counts as much a single as any other single (be it promo or commercial) that's been released IMO.