also her scaling with nunu and her great pushing ability. it doesn't matter if she "falls off" if she's still bewilderingly ahead of your carry because of how bad she trashed her lane
Nunu isn't exactly godly anymore.
And against some-one like Tristana, she needs to trash the lane, and midgame, so badly that she has 190% of Tristana's DPS [Unless I'm mistaken], else Tristana will just pop Rapid Fire, get a 90% boost to her AS, and equal out. Tristana even out-ranges Cait late.
Against hypercarries Caitlyn has to win lane by an amount that is pretty much unrealistic unless the other side is just bad and can't avoid dying by farming at tower and playing defense. Otherwise she just gets leapfrogged by 20~25 mins.
Hell, the only thing Caitlyn actually has going for her early IMO is her AA range. Graves and MF have more burst and outright kill potential. Draven's AA's and all-ins are better.
But that's just my exceptionally anti-Caitlyn view on Caitlyn. I just really don't like her, and fail to understand why she's so popular with her low kill potential and bad mid~lategame compared to most carries. Especially with Nunu out of favor atm. If you want to shut lanes down, I'd rather take Taric/Graves, Taric/Draven or Taric/MF.