The LED doesn't have a forward voltage up to 10V, it's the Cmos blinker circuit in it that operates from 3V to 10V like any ordinary Cmos IC.
I suspect that it doesn't need a current-limiting resistor since the Cmos circuit in it will limit the current. It will be at its max of 30mA with 10V, its nominal of 20mA at 5V and hardly work at 3V.
Somebody said to use a 1k resistor as a current-limiting resistor. Then for 20mA it will need 20V more!
4 Electros,
The site that you mentioned is stupid. They have a chaser project that they say lights one LED at a time, but they use a separate current-limiting resistor for each LED when only a single resistor is fine. Put the single resistor in the common voltage feed to the LEDs to reduce their current from about 12mA without a resistor.