Maybe those countries would find themselves in a similarly bad state (or worse) without those resources. Maybe their bad state is due to historical reasons - being former colonies with very little power on the world stage - and resources just couldn't help much.
Countries with a dominant resources that only found them when they were already developed don't suffer from the 'resource curse'.
In such cases not having resources doesn't mean you turn into Switzerland or Canada rather it means that it will be harder for one dominant dictator to hold on to power. In some African countries that are now proto-democracies, dictators simply couldn't hold on to power without easily available resource base.
Bruce Bueno de Mesquita work in 'The Logic of Political Survival' and ' The Dictator's Handbook' is quite interesting.