Alek,
I knew somebody would raise the prepaid tickets issue

The fact is that if I get on a bus in Munich sans-billet I can buy a ticket to complete my journey to any part of the city with any mode and only pay by zones travelled through. You can't board a bus in Dublin and do anything approaching that. You have to find a newsagent that sells tickets. This is simply NOT convenient, especially outside business hours or in places that are simply miles from the nearest shop.
You can't even buy a one day ticket from the driver on BAC. They do this in Glasgow (which also has pretty rubbish integration by international standards) where you just pay the driver £2.25 and he gives you a ticket that has the date and "all day" printed on it (from exactly the same bog standard 15 year old wayfarer ticket machines). How simple is that? Why can't BAC do that? Why must I go to a newsagent to pay BAC their money for a 1 day rambler? No excuse is good enough for these failures.