To state the obvious: iTunes music downloads are down while downloads of apps are up sharply: 35% year over year and 50% in December alone.

It’s tempting to suggest, Dediu writes in a post called Of bits and big bucks, that music downloads are suffering from the rise of music streaming services such as Pandora (P) and Spotify.

But what’s really changed, he believes, is how people are spending their time.

“Consumers have a fixed time budget, a more rigid constraint than their spending budget. Competition for a slice of a consumer’s time budget is far tougher than competition for a slice of a consumer’s wallet. So what’s amazing is that apps have successfully grabbed a share of this time budget.”

For now, apps are mostly filling downtime or “boredom.” But as the experiences they offer become richer and more compelling they could move upmarket into Hollywood’s territory — with casual gaming and social media apps, for example, become increasingly addictive and taking over time that used to be spent watching TV.

“This is the insidious march of a disruptor,” Dediu writes. “It gains a foothold in a context where it has no competition and then relentlessly gets better, eventually displacing the far better suited alternatives. This is what I believe is happening with apps. They are asymmetric in their competition with established media and as a result they are easily ignored and brushed off as irrelevant competition. That is until the incumbent media sees a sudden drop in consumption. Even then, the culprit blamed is not the upstart but some structural issue…

“The angst and trauma suffered by the media industry when dealing with what could be seen as a trivial change in the encoding of content [i.e. from analog to digital] are the stuff of lore and legend. Moving to apps could be even more troubling. Mainly because there is already a distribution channel in place. And it’s owned by a set of companies whose motives and business models are completely different.”

LINK: Of bits and big bucks.