The connection is that the observations at both airports are still (but for how much longer is unclear) carried out by Met Office observers, rather than ATC staff using SAMOS (Semi Automated Met Observation System).
When ATC use SAMOS it will default (IIRC) to 9999 (10K+) when appropriate, whereas the human element will provide the empirical data and that is what is broadcast on the ATIS.
I think the Met Office like to record information as accurately as possible for their own records, rather than more generic data used by aviation and so the ATIS broadcasts will reflect this data.
On the subject of CAVOK, I remember a Big Airways pilot complaining that he'd told the passengers it was sunny because it said CAVOK on the ATIS. Fact was it was overcast at 5500 and we hadn't seen the sun for days!!!! I think he was a little embarrassed! Maybe we should report a "sunny CAVOK" or a "cloudy CAVOK"?
