I was once horrifically stung (what I realize was a very long time ago) with an Abit "audiomax" soundcard that came with my motherboard. Quite horrific interference amongst the many problems. In a fit of pique I bought an Asus Xonar that solved all my problems immediately.
Since then, I've been through a few motherboards, but plugged that Xonar in, and it's definitely 'better'
Now if I didn't have that Xonar, then I'd be as happy as the proverbial Larry with my on-board sound I can get today. On-board sound is quite definitely 'good enough' now, but seems a shame for people not to realize (if they care) they can make it a great deal better for a pretty low price.
And, I've carried this card with me for quite a while as my GPUs have come and gone. The price I've paid for my slightly better sound is now practically nothing per year.
I think people still care about sound, but it's just another check-box on your slightly more pimped mobo - in much the same way as a I got a deluxe board with an Intel network adaptor in addition to the Realtek.
It doesn't really matter that much, I don't expect most people to care, but to say that on-board is good enough for all simply isn't true.
My current on-board is wired to my desk speakers for the day to day stuff I want to listen to, and the Xonar is connected to my silly-number-of-speakers gaming headset.