By fixing it instead his wife will now be frustrated with every other colour wheel that uses the de facto standard behaviour.
Also, it should only jump/slide to a higher saturation if the saturation is 0, otherwise moving around the colours with a fixed but non-zero saturation wouldn't be possible.
If enough users feel the same way as his wife, his competitive advantage will be so much bigger.
This is why some programs are considered easier to use, or even "better" than others. It's the sum of these tiny little behavior differences that add up to a better user experience.
Over time, some of them end up being standard. This is evolution at work.
Of course, if he can find an unobtrusive tweak (as it seems he did) which maintains the standard behaviour while eliminating a failure mode, then good on him and it deserves to become part of the standard.
[1] never use a big word where a diminutive one shall suffice!