I honestly can't think of any legitimate reason they wouldn't ship to the USA. Unless of course they don't want to make any money. Sales to the US would outnumber those to Canada 99-1 easily, regardless of what the product is. It's also cheaper to ship to the US than it is to ship within Canada with Canada Post. If they do enough volume with UPS, they can obtain discounts to ship to the US that they'd likely never be able to get for shipping within Canada. Etc etc...

Let me know if you run into any issues placing your order and I can definitely handle re-mailing for you if you need it.