Surely, the celeb and paparazzi world is akin to high school: wearing the same dress is social suicide. However, if the dress is that hot, like the Lanvin Spring 2010 one-shoulder calfskin dress, I'm sure J. Lo and princess RiRi will get a much deserved break.
Implications - Personally, I think the dress worked much better on J.Lo than it does on Rihanna. The ruffles in the dress are more prominent in J.Lo's version and it gives off a more sophisticated vibe in comparison to the Rihanna photo.