The vast majority of Avr's use time delay because its cheap and easy to implement when your signal is already in the digital domain.
The vast majority of subs use phase shifting because its cheap and easy to implement when your signal is already in the analog domain (though with the price of plug and play dsp's continuing to fall, there may come a time when a single multipurpose drop in chip actually costs less than a few opamps and such... who knows).
Time delay is technically superior, but both work well enough for sub duty.
