on the normal circuit the voltage available to the LED gets less and less as you reach the last LED, so if you're using the same resistor on each LED, the current gets less.
The JFET and resistor set up creates a constant current so each LED get equal current regardless of voltage, (with in reason).
Kinarfi
That particular arrangement has always been a favorite of mine for constant current needs and when charging a cap with this set up, you get a straight line charge up instead of the usual 63.2% time constant curve.
Kinarfi