Yes, Yes, Yes, Maybe, and
No, you've learned an important poem about purple cows.
Gourand shading is wrong. However, you usually will not notice because the transition
in colors is very smooth (And we don't know what the right color should be anyway, all we
care about is a pretty picture).
There are some cases where the errors in Gourand shading become obvious.
- When switching between different levels-of-detail representations
- At "T" joints.