The short answer is they don't, most lifters deadlift more than they squat. However, some things do affect these numbers.
If you go raw, there is a very significant majority of lifters that will pull more than they squat.
The lighter you are, the more likely your dead is better than your squat. Once you get to about 242 or so the numbers tend to even out and at SHW generally those lifters can squat more than they pull by a little bit.
The rules. PL feds differ a lot on squat depth. If you just go bottom of the leg parallel that allows lifters to go ultra wide and squat a ton. If you go IPF depth then you can't go super wide and so it changes the leverage and squats get much, much harder.
Gear - knee wraps and a squat suit help a whole lot, again even more with a wide stance and a shallow squat. DL suits only help a little bit.
To highlight, here is a quick list of lifts. These lifts are the 10th ranked lift on PL watch for 2010 men.
148 Squat Dead
Raw 407 501
Single 501 530
Multi 525 501
Raw 600 670
Single 685 683
Multi 771 660
Raw 750 735
Single 810 727
Multi 903 683
Single is single ply gear, multi is multi ply gear and usually those feds don't require the deep squats. Hope that sheds some light on the question.