Lat pull downs vs pull ups

[Fat Bill Dwyer]

So then we have most saying pull ups and some saying pull downs. Interesting. There has to be some difference between the two. What confuses me is that If I did the same amount of weight on the lat pull down as I do with pull ups (210lbs) I wouldn't be able to do as many pull downs as I could do pull ups with the same weight. This is what I can't get my head around.

I think this might be because of excercise specificity. You get good at what you train properly. Maybe you do really good pull-downs and have adapted to them well. Also pull-downs practically beg to be "cheated" on. Not that this is a bad thing, just saying you can get the bar down using muscles you couldn't use to get chest up on a pull-up.