There is a page on the wiki called "Platform Frame Rates",
http://tasvideos.org/PlatformFramerates.html
The NES frame rate (60.098813897441) seems to be calculated perfectly:
Master clock = 236.25 * 1,000,000 / 11 (21477272.7272727...)
PPU clock = master clock / 4 (5369318.18181818)
scanlines = 262
dots per scanline = 341
dots per frame = scanlines * dots per scanline (89342)
framerate (no skipping dots) = PPU clock / dots per frame (60.0984775561123)
framerate (skipping 1 dot every other frame) = PPU clock * 2 / (dots per frame * 2 - 1) (60.0988138974405)
The NES uses dot skipping every other frame to remove one PPU dot, so the frame is one dot faster than otherwise. This is done to make the colors look better.
In order for the SNES frame rate to match the NES frame rate, it would need to also use dot skipping. However, I cannot find anything suggesting that the SNES uses dot skipping. This would make the frame rate be the "No Skipping Dots" value (60.0984775561123) rather than the "Overall" value (60.0988138974405). This is a difference of 0.02s per hour.
