Different publishers. It looks like one of the books that's Public Domain in the US due to their differing copyright laws (says it was written in 1926, so it might fall under that "copyright not renewed" clause) and people have been repackaging it for sale.
You can probably find it free on Project Gutenberg or Google. If it's that old, possibly the author has been dead long enough for it to also fall under Canada's Life+50 public domain rules, too.
ETA: Well, what do you know?
He actually does become public domain in Canada as of Jan 1st, 2011. Happy New Year!