I recently just beat the game on the Wii Virtual Console and the ending was just Mario, the Princess, and Luigi standing there. Does nothing else happen?
After the credits roll and Mario/Luigi, Peach, and Yoshi make it all the way back to "Yoshi's House" and the eggs hatch, it shifts to the tableau of Mario, Luigi, and Peach (that you mention).
For the SNES and virtual console version of this game, that's all there is to it -- there's no new game plus option, and no way to save the game after beating bowser. The Gameboy advance version of Super Mario World (It was rereleased as Super Mario Advance 2: Super Mario World ) however, featured additional content after the game ended while collecting all the dragon coins. But, as this was specific to the gameboy advance port of the game, yes, that final tableau is really the end.
Edit: Actually, I'm not positive about the GBA port. It depends on whether or not Bowser's castle level has dragon coins, I suppose.