Your statement is only true for old technology batteries such as Ni-Cad.
For Li-Ion Li-Poly, there's no need or should I re-phrase, NEVER to let your battery die off. It'll kill your battery in no time.
I have to suffer the consequences with one of the Motorola smartphones and the ori battery died just right after 6 months, which the warranty only covers 6 months.

After that, I never do that to my PSP, laptop, other handphones, and the battery is going strong. Even my 6600 which I bought since it first launch, the battery is still alive and kicking; I'm not using it, just using it as alarm clock, but it can last at least 2 days.

With the new technology that cuts from overcharge, the risk is LOW from exploding. But you can't ignore the risk, if it have a chance to explode, your phone is a gonner.