Youtube recompresses the video, so chances are that already present artifacts (MPEG-1 is prone to that) are emphasized and amplified. With Argo's method you'll make sure that artifact/noise levels are low which should yield a much better quality output. Actually you should avoid MPEG-1 except for extremely low resolutions/bitrates as the quality is quite lousy.
Additionally, they're probably unable to handle MPEG videos with weird frame rates - I'm not at all sure if the standard even allows for this. If you have no frames in-between, just double every frame.
