Well, my $28 Sinnoh set arrived today. I've checked my Paypal account, and the right amount's been charged, so I've gotten a massive bargain out of this. I was going to sell it - but I noticed on the back of the box it listed the aspect ratio as being 4:3 and 16:9. Now, I also bought the Black & White box set on Tuesday and realised that the episodes on there are the "American" cut (with Who's that Pokemon included in the middle of the episode, not with half just before the credits), not the "international cut" - so I thought maybe, just maybe, that would be the case with this Sinnoh box set. It is, partly - the widescreen Galactic Battles episodes are still cropped, but the Sinnoh League Victors episodes are in widescreen, and Playing the Performance Encore is the version without dub music.
ETA: Also worth noting - the discs themselves are housed in cardboard sleeves, but were shipped in individual plastic bag-type slips (like the kinds you'd find on vinyl records) inside the sleeves. The plastic slips themselves are pretty flimsy and have one of them has torn after taking the disc out 3 or 4 times - but it means the discs themselves haven't been scratched or gotten any packaging glue stuck on them while in shipping or on retail display. An improvement, I guess, considering the complaints the Johto set got.