Lanefan
Victoria Rules
I've never seen an entire party do it but I've played with and DMed individual players who, even in an xp system that rewards risk-taking, refuse to take any risk unless forced to; instead allowing others (of whom, when a player, I'm usually one) to take the risks for them. Result: the risk-averse live and gain the rewards while the risk-takers get maimed or killed or whatever. (on topic: this all assumes a setting where violence is common and characters can die)I've never heard of a party that was ok with just sitting around regardless of how their XP was metered out.
In a system that gave xp or levels without regard for character actions or risks taken, the risk-takers would have no incentive to do so and the whole thing would grind to a halt.