A secondary part of this is; where do spell casters get their components from? In some settings then it would be reasonable to assume magic shops in large cities for certain things, but who collects them, what about settings where magic is less common? 'Course in D+D it's nowhere near as bad as in Warhammer FRP where the components involve parts of things that can kill off pretty much anyone, and that's sometimes just level one spells.
It might be relevant to say what got me wondering about the issue. The most recent FAQ from the Wizards site has a short piece on Hallow/Unhallow and how that would be difficult to counter because of the components. So really I suppose I'm thinking about whether dropping components has made things too easy on the PCs.