I am on stock 2.1 and this morning wen I went onto the market, it showed the original android market that the 2.1 update gave us. I guess it randomly rebooted or rebooted for a reason and after I went bak onto the market after reboot, it looked like the market was the market on preclair 1.2.1, but with a new tab called" related" wen u view an app in a market.
Google has been pushing out the updated Market to pretty much everybody except those still using Android 1.5. I'd say it's natural. It probably updated itself when you went into the Market.