In the U.S. there are 37.9 million devices in use that run Apple Inc.’s iOS mobile operating system, which include the iPhone, iPod Touch and iPad. That’s 59% more than the 23.8 million devices that run Google Inc.’s Android mobile operating system, according to new data from web and mobile measurement firm comScore Inc.’s comScore MobiLens service.

This number is significant because research firms to date have been reporting smartphone share and tablet share separately, and ignoring the iPod Touch. Most research firms have reported that the number of smartphones running Android has surpassed the number of iPhones. But that’s only smartphones. ComScore has added the iPod Touch mini-computer and the iPad tablet on the one side and Android tablets on the other, producing significantly different market share results than when comparing smartphones alone.

What this means for retailers is that when considering where to focus mobile app resources, they need to consider that developing for Apple’s iOS will give them greater reach. An iPhone app works exactly the same on an iPod Touch as it does on an iPhone. And iPhone apps can be used on iPads, as well. However, they appear on an iPad screen at the size of an iPhone screen. IPad users can press a button to make the iPhone app the size of the iPad screen, but the image loses a little resolution.

Regarding the iPad, comScore also released age demographics on owners of the tablet PC and owners of all brands of smartphones. 7.6% of iPad users and 6.3% of smartphone users are ages 13-17, according to comScore. Advancing in age: ages 18-24, 15.2% iPad, 16.9% smartphone; ages 25-34, 27.0% iPad, 27.4% smartphone; ages 35-44, 20.3% iPad, 22.1% smartphone; ages 45-54, 16.4% iPad, 15.3% smartphone; ages 55-64, 7.3% iPad, 7.4% smartphone; and age 65 and older, 6.2% iPad, 4.6% smartphone.

The demographic profile indicates very similar numbers between iPad owners and smartphone owners, and shows that the greatest concentration of users of both types of mobile devices is between ages 25 and 44.

Of tablet computers, the iPad is the kingpin, according to a new study from ABI Research. In 2010, 85% of tablets in use were iPads, the firm says. Samsung’s Galaxy Tab ranked a distant second with about 8% while Archos’ Internet Tablet registered at a scant 2%.