All modern browsers support the HTML5 audio tag.
Yeah but that isn't really good enough to play sounds in (for a game).
I disagree, it's not the best, but it's decent enough for most games. Most HTML5 game engines use the audio tag. My game uses a good amount of sound effects and background music just fine with the audio tag: http://cityfortyone-mattgreer.dotcloud.com/dragonPlunder/
However making music is an art not all programmers have mastered, so most would likely skip that step.