Missing wood for trees. RGB displays are deliberately made to be 'good enough' rather than 'great'. None of them can display whole areas of the visible spectrum [1]. Before taking issue with tiny amounts of visible banding, just maybe it would be better if monitors could actually display a reasonable amount of the visible spectrum...
It's quite obvious that for a gradient from 0x33 to 0x66 (one component), there are simply not enough distinct values to prevent banding. In this case, the range is 51 different values, for a gradient that's maybe spanning 500-1000 pixels. It really looks quite terrible.
I should point out that the area of a region in that diagram does not correspond with the ability to distinguish colors in that region. The diagram is misleading, but your point still stands.
[1] For a reasonable graphic example http://en.wikipedia.org/wiki/File:CIExy1931_srgb_gamut.png where grey is the entire visible spectrum and the coloured areas are the standard RGB colour space.