I generally animate/render out at 25 fps (so it matches with PAL, just my settings) then if I'm going to compress for say the web I might then drop the frame rate of the overall file (in the export settings of the programme i'm using) to get a smaller file, I wouldent use the frame rate to determine the speed of an animation, unless its a slow mo captured at a very high frame rate then dropped to 25 fps in the compositing/editing.

I think the actual framerate for NTSC is 29.97 or something like that, but its generally rounded up to 30 fps.

Might be due to the imperial system being used ft/inches then converted to metric or something???