Naw. You can carry games. You just have to be a really powerful carry and get an explosive head start on everybody else so you pretty much just beat their asses down midgame. Ranged AD carries are pretty damn good at this once they have Infinity Blade+Phantom Dancer.
Also, I just played a match as Zilean. Ashe and I go bottom to face off against Karthus and Shaco. Both of them were pretty terrible. Shaco just hid in the bushes a lot and Karthus could never ever hit me with his Lay Waste. I zoned them out with time bombs and would've stopped their exp gain entirely if Ashe hadn't kept pushing the lane dumbly by autoattacking. Actually, Ashe would've been a lot deadlier lategame had she actually gotten last hits. I was setting up last hits for her, in fact, but I still had a higher CS by midgame. Karthus and Shaco actually got me low a few times. As soon as I got away from Karthus with only around 100 hp, I hit the Chronoshift just in time for Requiem.
Second time I got low from Karthus was around lategame. Well, not low from Karthus specifically. Dr. Mundo up top was getting beaten down by four champions, so I rushed up there to help him. We both ended up running away from four champions crazily, surviving only due to Zilean's movement speed buff. It was hilarious. Dr. Mundo managed to get away, but Karthus hit me with Requiem. I wasn't fast enough to stop it.
Clairvoyance is a lot more useful than I initially gave it credit for, too. Stopped like two-three ganks through Clairvoyance.