The garden hose vs. fire hose is actually a bad analogy.
If you hooked up a fire hose to a standard garden spigot, you'd get the same amount of water coming out the other end as if you used a standard garden hose.

If a hose's diameter (like a wire's gauge) meets the minimum requirements for preventing loss of pressure (signal), anything greater is unnecessary. Even 2x6 will tell you this since he loves his very thin Mapleshade speaker cables.