[lenkite]

Did you observe that in ALL your examples you have given only 2 colors at a time ? This is because it is extremely difficult to visualize 3 colors additively together. Doing it with trial and error and "try it and see" is painful. Too much wasted time. (Well..there ARE some people who are expert at mixing 3 colors - they visualize the full RGB cube and magically output 3-color permutations off the bat after looking into space...)

Whereas, Hue in a 360° axis gives you a braindead-simple, direct color access - cycling across the color wheel with well-defined, named and representative colors at regular degree intervals. The 2D visualization of a circle is far easier.

You grab your primary color - hue and then you adjust your saturation and lightness (which is across a simple, linear semantic axis) to get tones and shades. FAR more simpler than RGB to get an elegant color palette going. You can knock out a distinct color palette for a site using HSL in ~5-10mins. Use a color-contrast tool against text to check accessibility and then you never pay attention to color again.