Well, regardless of whether your own machine ever touches those root servers, they are actually quite necessary.
DNS works by going from general-to-specific. The root servers manage a DNS zone that is really just "." (yup... dot).
So if you look up www.freerepublic.com, what you don't see is that domain names actually have a . on the end... just isn't needed really, it's assumed. :)
To lookup it's IP address, a DNS server would first find the servers that handle . (the root servers). Those would tell you where to find the servers that handle .com., and those servers tell you where to find freerepublic.com. and then it tells you where the server is for the hostname www in the domain freerepublic.com.
Rocket science, hardly, but just goes to show that without the root servers, we'd be screwed.
Practically speaking, any DNS server along the way can "cache" the data... I mean, DNS servers don't change all that often, so most servers out there, including the ones your local ISP uses, will cache data for hours, days, even weeks or months. I always get frustrated when I have to make a DNS change and there are servers out there that ignore my time-to-live settings and keep spitting out their invalid cached addresses. Urgh.