SF,
The issue of getting back down is equally true in all of the countries that do allow VFR flight above a cloud deck by plain PPLs. They admonish pilots to use good judgement and planning so you are sure it is a localised cloud deck an can get back down. This difference in rules doesn't seem to show up in a higher level of safety in the UK. I suspect the logic of SF and IO540 was used by the CAA drafters who came up with the rules.