Most modern distros come with pulseaudio by default, which means I'd guess that over 90% of linux users use pulseaudio successfully. I've run workshops helping people install linux on their machines and I've never run into a system where pulseaudio did not work that alsa did.
Which means they almost certainly include libasound.so, because PA still depends on ALSA in the kernel. Even in the case of distros that only use the ALSA emulation interface for PA, the traditional ALSA interface is still provided. Lots of software would break without that support.
It's more accurate to say most distros support both PA and ALSA by default.
> use pulseaudio successfully
Note that "successfully" doesn't imply "enjoyably" or "preferentially". I still hear complaints regularly from people that hate newer (PA-focused) distros that introduced a lot of latency problems. Movie audio sync became inconsistent (hundreds of ms latency, very high variability), and UI audio cues playing up to 3s (3000ms) after the visual changes.
This is what bothers me so much about discussions about PA. There are legitimate problems with it, and whenever someone mentions them, everyone else chimes in to say that they are the minority, that they are doing it wrong, etc etc. This is how polarization happens.
I've had a much higher success rate with alsa ootb.
Ehh...... I'll disagree with that. I have ~50% success rate of it working on my devices in the past 5 years.