It's one of those "I bet someone got a nice bonus for that" ideas that destroys user trust: http://blogs.msdn.com/b/oldnewthing/archive/2006/11/01/92244...
Slashdot's audio ads don't wait 10 minutes to start. Slashdot's much hated auto-refresh "feature" is to blame.
It periodically refreshes the page and brings you a new crop of ads, some of which might be audio ads.
The auto-refresh "feature" merely exists to increase their ad revenue. Nobody I know likes the auto-refresh feature, as it just causes you to lose your place on the page.