l know this is old, but the graphics are run exactly the same as on 3DS and DS.
The 3DS runs DS games as a regular DS would, and l guess looks "better" because the 3DS screen has higher resolutions than the older DS (for better quality), but since DS games were made for DS resolutions, pixels and everything shown on the 3DS screen will be stretched or look a little fuzzier, kind of like comparing a game played on a DSi XL screen cause the screen is physically larger without having a larger resolution.