This was my thought as I observed an excellent Kinder math lesson at one of our schools recently. I'm not surprised this is still taught in schools or as part of the fantastic Mathnasium curriculum. It's wonderful as a concept: it's one of the first examples of the idea of "half" that we use in elementary math.
Here's the problem: nobody uses half dollars any more. It's akin to using $2 bills, 8-tracks or floppy disks for real world context: it doesn't work, because nobody uses those in the real world any more. It's what Dan Meyer and Jo Boaler refer to as psuedocontext; a completely unrealistic problem, posed as a "real world connection" that isn't. Why are we still teaching it? Because it's convenient? Because Kinder kids don't know yet that the half dollar is obsolete? I'm sure many notice that when people have pockets full of coins, no one seems to ever have any half dollars on them.
On a similar note, what are teachers going to do when there's no more pennies? How long will it take until pennies disappear from circulation, and then how much long will it take for it to disappear from classrooms (if ever)? When they're gone, what crutch will we use to teach ones? Or will we just skip ones when talking about coins and just use them when we're talking about dollars?
I'd rather schools ween students off the half dollar and at least consider using the dollar coin more. Sure, they're not ubiquitous either, but they're used significantly more than half dollars. Just as the penny will likely die, paper money might be replaced by coins (as it is in many countries around the world already) in our children's lifetime, so doesn't it make sense to at least introduce something at least slightly more relevant?
As educators, we've got to constantly reevaluate the real world examples we use in every subject, at every grade level. It doesn't take very long for them to become examples of a world that no longer exists.