Well, take any NES game, update graphics and sound resources to modern standards, and change nothing else, and the game is suddenly at least 256 times larger.
True, updating graphics/sound resources would significantly increase size, no dispute.
Edit: Actually a more interesting question is: if you take a modern 2d platofmer and significantly shrink or even remove the graphics/sounds, would it be small enough to be run on older game platforms? (I don't have the answer to that)(and to be fair, graphics size reduction is still a form of optimization )
I was reading this article a while back on making McKids: http://games.greggman.com/game/programming_m_c__kids/ since I was starting a 2d platformer. There's still a large number of code optimizations that made these platformers possible back in the day; optimizations which most modern games don't have to worry about (though admittedly not all are size optimizations)