Pulseaudio did expose a lot of bugs in alsa that needed to be fixed in alsa. IIRC they are attempting to move from scheduling sound with the soundcard's hardware interrupts to an entirely cpu based method. I can't remember exactly what the technique is, but it allows for better latency control, better mixing of applications which make different buffer size/latency demands, and consumed less power overall because of increased flexibility over have the processor sleep. Pulseaudio has been buggy because in many cases they have been the very first people to ever make use of some of the more esoteric parts of alsa. Those parts also lacked proper documentation and many drivers didn't even bother with a proper implementation.
