I saw something like this at Sakuracon this year. I'm quite certain no direct copying was involved, but with a bunch of the vids that had scenes from EVA, Kenshin,Bebop, or Trigun, you saw cuts to the same scenes over and over.
I believe a big part of this is simply that there are only so many scenes in any given anime that have an unusually high emotional/dramatic content, or are funny, or just plain cool looking, that they stick in the minds of the creators while either planning their vid, or scanning for footage in the clip window.
The differences came with the song selection,editors skill and ability, and at least a little bit, the quality of the source. (nasty, macroblocked, mpeg4 fansub source looks like ASS, kids!
Overused scenes/animes aside, there were clearly excellent vids there that dominated the competition. (like the Kenshin/Enigma one)
I'm sure a few tards have just swapped in an audio track, but I've yet to see it.
My Eyes Are The Victim's Eyes.
My Hands Are The Assailant's Hands.