Here's another way of looking at it: with the possible exception of the bath-tub (which has it own rules about tap orientation anyway), I expect the kitchen sink gets the most use in any household. Nine times out of ten you go to the sink carrying something in your hand, be it a kettle or a plate, etc. Most people are right-handed, therefore that object will be in their right hand, leaving their left hand free to turn on a tap. The instinct then is to reach for the left hand tap, or in the case of monobloc taps, the left-hand lever, where you risk getting water on your sleeve if you do otherwise. I would argue therefore that having cold on the left is more convenient. But there is something more important at stake - energy. When it comes to washing and rinsing, if it is so much more practical to reach for the left hand tap every time - even though you don't necessary need hot water - that's x amount of energy being wasted, often most of it not even reaching the spout. Multiply that by millions of household and millions of hours and you've got a case for breaking with tradition.
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