Why do people still say that? It's absolutely stupid. Moving is a part of League of Legends, like 95% of the games. It's not something you can buy with RP so you're better than everyone else in the game, so they would call you "RP run noob".
If I'm being chased by a bloodlusty Lee at 100% hp, I'm not going to be like "Bum this, running is cowardly, I'm gonna stand and fight him!". Just, what? I would have accomplished nothing, the small percentage of hp I got off of him will be back right as he recalls.