If you take another look at the figure, the highest correlating factor isn't whether the "gadget" (by which they mean consumer technology, not any specific device) is for "consumption of entertainment" or "communication or production of media", as the text of the article suggests. It's simply how complicated the technology is--dare I say, how innovative the technology is--and the reason is simple: the more innovative the technology, the longer it took from first being "on the market" to becoming mature enough to be widely adopted.

(How does one count length of time "on the market", anyway? What counts as the first cell phone "on the market"?)

So what this is really saying is: the more advanced the technology, the longer it takes for the technology to go from early-adopter to mass market.