Yahoo Japan's 'English auction' format is pretty much what most people think of when they think of an auction - the auction remains open until no higher bids are made.
Given a large enough group of buyers, this is just plain more efficient than eBay's 'auction by the candle' format in identifying a true market valuation.
eBay's format is more exciting, though - setting up a snipe, watching the clock tick down - it's adrenaline-inducing stuff.
Since it's more exciting, it may draw more buyers into the marketplace, increasing the market performance vs. YJ's better format (but with fewer buyers).
YJ better allows you to adjust your valuation in the face of market competition. If everybody wants something, you might be willing to pay more than your initial valuation. On eBay, you don't get that chance.
But on eBay, you can catch people flat-footed, trying to pick something up below market value.
In the end, I don't know which ends up a better model, but I shop both - mostly YJ.
2 hunting grounds are better than 1, and YJ is pretty darn fertile when it comes to Seiko, especially vintage Seiko.