Publishers have devised a number of clever ways to eke as much money out of gamers through digital sales as they can, ranging from online passes for online modes to season passes for downloadable content. A new study from market-research firm Newzoo that tracks DLC, preowned sales, and digital distribution offers one explanation why.

The good news? DLC revenues are on the rise.

According to Newzoo's findings, of the 82 million Americans who say they play console games, only about 36 million of them, or 44 percent, buy games at all. Instead, Newzoo found that games are more often than not shared between families or groups of friends.

Newzoo's study also found that of those Americans who do spend money on PC and console games, 85 percent also pick up preowned games. For 25 percent of game buyers, at least half of their budgets go toward secondhand purchases, according to Newzoo. On average, US gamers spend about 23 percent of their gaming budget on used software.

As noted by Newzoo and others, the secondhand issue is a boon to retailers but problematic for game makers, as publishers see no revenue from used sales.

The upside, the study notes, is that revenue generated from DLC sales on consoles and downloadable PC/Mac games is steadily growing. Newzoo found that downloadable PC/Mac game sales in 2011 have already surpassed boxed sales in 2010 in the US.

Further, Newzoo expects DLC spend to reach $960 million this year in the US. That number increases to $1.75 billion when DLC spend from the UK, Germany, France, Spain, Italy, Netherlands, and Belgium is factored in.