Hi,
It depends on the definition of distance, to sort point based in "distance" you can use any function that define a metric which have the following conditions:
d(p1,p2)>=0
d(p1,p2)=0 <=>p1=p2
d(p1,p2)=d(p2,p1)
d((p1,p3)>=d(p1,p2)+d(p2,p3)
But you have to take in count that not all the metric are equal or induce the same ordering over the point set, the metric you are using DOES NOT set the same order that the Euclidean distance (the length of the vector between p1,p2). By the way the distance you are using is called Taxicab metric or Manhatan distance and it's useful in some situation, by example to calculate the "distance" in a grid when you can't take diagonals.
Saying that, Owen it's correct in that you don't need to use square root as squaring (the inner part of the euclidean function) is monotonic (in rigor monotonic increasing), and square root is also monotonic (i.e they preserve order under Euclidean metric. distance).
Gaston Nunez