You may have to point me towards a source here but as far as I'm aware, there is no unified EU-wide visa policy. If you are referring to the Schengen requirement that those who enter visa-free only stay a maximum of 90 days in any moving 180-day window, then indeed, onward travel to the UK is considered as fulfilling the requirement of exiting the Schengen Area.

Edit: it does come to mind that there is a bona fide EU-wide visa policy in that EU as a whole coordinates bilateral visa waiver programs with other countries. However within the EU, distinctions between Schengen Area and non-Schengen states are still very much made.

Edit2: now that I've dug more into it. It seems that even within the Schengen Area, certain rules differ. For example, the Schengen treaty does grandfather bilateral agreements in force before the treaty came into effect. Thus, a US citizen may stay in Denmark for 90 days in any 6 month period regardless of how long they've spent in another Schengen country with exception of other Nordic countries. And New Zealand citizens can stay for 90 days each in many EU countries regardless of Schengen rules.