Being a guy with a pure Canon kit that probably tops $25,000 in total personal cost...that's very frustrating. Now, instead of just being able to pick up a new Canon body with ergonomics and functionality I already know how to use without even thinking about it, I have to expand my kit. That involves even more cost, a new set of lenses that largely duplicate what I have, learning a whole new camera system, etc. I like simplicity...one brand, one set of lenses, one type of button placement and menu system. It just sucks.
The alternative though is there being no difference between the brands, ergo no competition. If you could grab a Canon 5Dxyz that equals a Nikon Dzxy, why would there be a Canon and a Nikon?