The difference between a piazza and a plaza

From the Guardian, architect Renzo Piano emphasises the importance of urban loafing:

http://arts.guardian.co.uk/features/story/0,,1647127,00.html

Through the London Bridge development, Piano wants to introduce the European idea of urban planning to the British capital, ideas which he characterises as understanding the difference between a piazza (good) and a plaza (less good).

"A piazza is not a plaza," fumes Piano. "The plaza is the theme park of the piazza; the plaza is the commercial version. A piazza is an empty space with no function. This is what Europeans understand." A space without function allows one to be "in the moment", he says, and to counter what he sees as a major flaw in modern life - the habit of interpreting all experience in the light of achievement, as a means to an end. We should, he thinks, learn to lighten up, and the creation of empty, purposeless spaces within cities might encourage that. "You don't have to struggle to give function to every single corner. You
can just wait and see and enjoy."