Actually, I think challenges are a pretty big deal for those of us who "secretly" must be number 1 on our friends leaderboard lists. I mean, I spent HOURS playing the worst pinball table ever created in the history of mankind "Rome" all because Al beat my score and sent me a "suck it" (that's me paraphrasing). And, I see him trying to beat my Star Wars score (not happening) each time he's logged in all because I sent a "suck it" (again, paraphrasing). Personally, I'm glad joker went PC only because I no longer have to obsess over his damn Robotron score. You'd think I'd have some Midway insider secrets on that damn gamn...but no...
Agreed, WoW does this a lot with events that only occur at certain times/days and sometimes people get special mounts or gear by participating (i don't play WoW so i'm relaying this 2nd hand). Its a badge of honor that you have this stuff and adds a level of scarcity that I like. I think the hardcore gaming community will also appreciate getting things that not 'everyone' can get.