I'm a translation & localization nerd by trade, and I'm sure that the reason that your top-o'-the-keyboard shortcuts don't work boils down to some sort of failure in localization QA. Speaking really vaguely, here: when you whack command-6 on an en-US keyboard, it sends some number to the OS, and the OS interprets this number into some kind of output. The OS developer (Apple, in this case) is supposed to standardize this stuff, and the software developer (Adobe) is supposed to get those numbers in some kind of standardized way. Without doing some testing, we have no idea whether InDesign is grabbing those values in a non-standard way, or if the keyboard manufacturer took a shortcut in driver development, or any one of a number of possible duct-taped hacky workarounds. I do that kind of testing sometimes, and I am sometimes horrified by the slipshod way in which many vendors fail to serve their users who aren't using plain-vanilla English computing environments.
Long story short - you've already figured out the real workaround, which is to associate your keyboard output with the functions you want in ID. However, you'll most likely need to make new shortcuts if you switch to a different hardware keyboard or key layout.
