Why PulseAudio can not mix multiple OSS program's sound output?

I have Debian Wheezy, but had the same experience in Debian Squeze beforehand: PulseAudio comes installed with graphical workspace (well, to be honest, I don't remember the exact aggregate, but Gnome depends on it, so it can come easy. I use WindowMaker), however apparently it frequently breaks (I had to frequently kick it with a killall pulseaudio), and is simply unable to reliably output multiple program's outputs simultaneously which are configured by default to use OSS (/dev/dsp).

I came to ask because being fed up with the situation I ripped PulseAudio off of my system, then re-configured every program I use to output through ALSA, if necessary, using aoss. Since then, the system works like a charm: nothing woes, and I can run everything nicely in parallel not complaining for audio (even a single stray OSS program fits if it happens). This is not like I would want (or except) to have a dozen of applications outputting sound simultaneously, just problems like any OSS application would "freeze" (such as an SDL based game I am developing) when Firefox was open with just a single site left in there having some Flash content (obviously needing the audio device) somewhere.

So my question is: How PulseAudio is supposed to give (at least) the same experience like I am having now with plain ALSA? (I guess it should, otherwise why in the first place it is there...) I mean what I could be missing here? I did not do any particular configuration on this field, I used it just how it came. Otherwise, if what I experience is "normal", then why PulseAudio is even there (begging to be installed with Gnome) the first place?