Sales-tracking analysis firm NPD has been paying attention to the number of digital video games being sold and has found that of all “full game” downloads being sold, half of them are mobile titles.

That’s a pretty big number, considering that lots of video games are sold download-only, including titles on PC and Mac, as well as on Microsoft’s Xbox Live and Sony’s PlayStation Network, plus portable game systems like the Nintendo 3DS and PSP. The numbers don’t include “microtransactions” like you’d see with in-app purchases and Facebook games, or downloadable content expansions for existing games.

PC World has the story, but also points out that NPD’s findings don’t necessarily mean that mobile is dragging in a ton of money. Full video game downloads for traditional systems can run anywhere from $5 to $60, whereas mobile games rarely get over $7 or $10. That generally means that a game like Angry Birds has to move a whole lot more downloads at $0.99 a pop than the recently released Portal 2 does at $50, as PC World mentions.

The study also found that of the 8,000 respondents, 60 percent said they were spending as much or more time playing games on mobile devices as they do on traditional gaming devices.

Another firm, ABI Research, speculates that app downloads will break 44 billion by 2016, according to a story from Pocket Gamer. Those numbers will be driven primarily by sales in the Android Market and on Microsoft’s Windows Phone 7 as they fight to catch up with Apple’s iOS platform.

So, even though mobile games don’t draw the same amounts as traditional game downloads do when they’re sold digitally, all signs are pointing toward continued huge sales in the mobile sphere. A huge portion of those sales will be coming from Android users, with the platform’s market share expected to hit about 50 percent by the end of 2012.

Among gamers, mobile titles are becoming a satisfying alternative to traditional games, according to NDS’ research. With all the numbers pointing at more Android games, more apps in general and more people playing and downloading, it’s only going to mean more developers working to take part in the market and more great titles to make up that 44 billion.