You can add both Finland and Denmark to the list of countries where it's considered a native dance tune. I'll try to remember to ask my Polish friends this weekend.

I have an old (50s, I think) Capitol recording of Ukrainian dance music which includes a tune that sounds suspiciously like "I'm a Little Teapot". I wouldn't be surprised if several simple tunes (ur-tunes?) either arose independently in more than one place or originated while tribes were still migrating through Europe.

Other explanations are possible, however. I recently heard a Danish band playing several "native" tunes from one of the smaller islands, which were clearly recognizable as Playford dance tunes. And I'm told that in Norway it's considered just fine to take contemporary Appalachian tunes, play them in the local style, and claim them as Norwegian.

By the way, I'm curious about the statement that Soldier's Joy is a hornpipe. I've always heard it played like a reel, fast and even.