all LEDs have an exceptionally low reverse voltage. It's is usually specified around a few volts in the data sheets.
Sure, LEDs have a rating which is much less than the PIV of a regular diode, but I don't recall ever seeing one with such a low rating that it can't withstand 0.6 or 0.7V reverse voltage, which is the most you could get with D2 acting as a clamp to limit the reverse bias.
Belt and braces, I guess.
[This message has been edited by pauluk (edited 10-30-2006).]
