Technically it won't need to be worried about, logistically it will.
You want Amazon to eventually support BTC right? Does their current system support .000001 precision?
Whether merchant X or Y supports bitcoin is up to them, if they see a profit opportunity, they will make it happen, no matter how many decimal places bitcoin has.
People do not work in isolation, seeing BTC's only via their BTC client.
They also talk about them, read about them, see such values displayed on potential offers to buy and sell, ...
Human factors absolutely should be worried about.
You guys are worrying about something that could only happen if bitcoin was widely adopted, fearing that it would prevent its adoption by new users. You see how it is a non-issue ?