LED mod diagram question

[jakxxx]

Can someone explain to me why the resistors go after the led in all of the online resistor calculators?  I always thought you were trying to limit the current before it hits the LEDs.  Logically this doesn't make sense to me.   Here is a link of what I am talking about.

http://led.linear1.org/led.wiz

with the data 3.6, 2.1, 20, 10

[bustinthejustin]

It doesn't matter as long as it's in the circuit.