'Differential pricing' within the Eurozone is a non-issue: you simply set a standard price.

My initial 'flyer' was to have a common stamp throughout Europe. Sjoerd pointed out that postal rates vary between countries. His argument would have been stronger had he chosen as examples two countries that are not both in the Eurozone. It would obviously be rather problematic to introduce a unified stamp when not only does the rate vary but so too does the currency in which it is sold. So I limited the proposal to countries employing a common currency, whereby the difficulty of foreign exchange would be eliminated. You then sell the stamp for the same price in Greece, Holland and even here in Finland, where we have the highest postal rates in the Eurozone. No problem.

All countries can of course continue to print as many of their own little pretties as they please, for those who like to paste them into albums or whatever. It's simply that having a stamp that you could stick on a letter when you're out of your own country without having to go somewhere and buy one would be equal to the advantage of having a banknote that you can pull out of your wallet and spend, without first having to go to a bank or bureau de change.