Yes. I suspect that because of the low number of residential ISPs there's less internet infrastructure in general and less competition. Who needs peering if there's only Comcast? You point out that networks can exist that don't serve residential customers, but who do they serve - mostly other networks which don't exist because they can't serve residential customers. The entire US is just the access region for a few networks to backhaul to NYC, Chicago and SF, not a full fledged network itself.