How are browsers handling it differently?
If they weren't on the public suffix list, cookies would be shared.
This also affect a myriad of other contexts that the browser applies against the public suffix list.
There exist people who disapprove of this behavior.
A few years ago I tried all two-letter ([a-z]) TLDs and found some others that were able to handle HTTP requests, but they were either just redirecting to another domain name (the ones I noted down back then don't seem to work anymore) or returning 500 errors (http://uz/).
These examples should at least demonstrate that there shouldn't technically be some special case for resolving TLDs. They work in normal web browsers, and presumably a lack of A records for other TLDs would just be some sort of convention.
curl http://ai
Apache's Hello world:
curl http://pn
ping tk
ping uz
ping cm
All others had this error:
curl: (6) Could not resolve host: %tld%