NATO is supposed to be an alliance, not a protection agreement. And what is the point of an alliance if your country doesn't have a worthwhile army? Why can't you be asked to hold up your end? Asking you to hold up your end is not "demanding tribute."
My country does have a worthwhile army and an independent nuclear deterrent. I am dismayed that you can imagine that the European Nato members can't field significant forces, that would be very insular thinking. Sure they don't have stealth bombers and super-carriers...
My country has also supported the United States in many of its foreign campaigns as an ally supplying manpower and materiel to Afghanistan and several gulf wars for instance.
The sub-text is that my country spends a great deal of it's 2% on American weapons, which is not true of some of our Nato neighbour's. When I hear the USA demanding more this is what I hear, 'spend more on US made arms' not 'build a better army'. That is why I call it tribute.
You must be from the UK or France, then. That means your country is very capable of designing and manufacturing world class weapons systems if you don't want to buy from the US.