Thank you for posting this. I've been trying to get this point across for a long time. Perhaps it will make more of an impression coming directly from a confused U.S. buyer.
I've been listing in $US on .ca for several years, however two things have invaded my "comfort zone" in that regard:
1) The fact that the .com cart causes serious errors if a .com buyer attempts to purchase more than 1 item from a Canadian seller listing in $US; and
2) The references by eBay staffers to a change in the not-too-distant future to forcing sellers on .ca to list in $Cdn.
For the above reasons, I've decided to switch to listing on .com, after all these years on .ca. EBay just can't seem to make their system work across the U.S./Canada border. 
