IMO,It's just like having two cars of different manufactures Each one drives different or offers maybe something the other don't. The end result is probably the same though.
Well, I can relate to that since I do have two motorcycles, but in my opinion, if you want to use that analogy, I'd say that it's more like having two different brands of RACE car. I Feel that one could accomplish more if they focused on one brand and learned to use it properly rather than dividing their efforts between two that are completely different in the way that they behave.
I'm fully convinced that if you put a good Canon body in the hands of someone who knows how to use it and a good Nikon body in the hands of someone who knows how to use it that the quality of the images from both are going to be virtually indistinguishable. I'm not touting the adage that it's the photographer and not the camera because a good tool is just as important as the knowledge of how to use it. I'm simply stating that there is a point where photographer and camera become one regardless of brand.
I'm also fully convinced that jumping from one brand to another brand simply because one feels that the "Other Brand" is going to make them a better photographer overall is misleading in most cases. For the vast majority of us learning how to use what we already have is going to yield better results than simply using another brand.
That said, I'm fully aware that both Canon and Nikon have some limitations with ANY of their bodies. Some Canon bodies may do certain things better than certain Nikon bodies, but at the same time both manufacturers have a large number of bodies to choose from. For example, I don't see that abandoning a mid-range Nikon body to jump to a high-end Canon body is a comparable switch.
But, to each their own. This is just my own opinion and everyone has to make their own choice as to what is best for them.