Patent firm Lodsys wants a cut every time little Timmy buys a new content pack for Pocket God.  Photo: Emmanuelle Bourgue/Flickr

Now the company has explained why it’s going after the little guys, instead of Apple: Lodsys says Apple has licensed the patent in question.

“The scope of their current licenses does NOT enable them to provide ‘pixie dust’ to bless another (3rd party) business applications [sic],” Lodsys writes in a blog post about Apple. “From Lodsys’ perspective, it is seeking to be paid value for rights it holds and which are being used by others.”

Incidentally, Microsoft and Google have also paid for licenses, too, according to Lodsys.

Lodsys sent letters last week to a number of iPhone app developers, accusing them of infringing a patent related to the usage of an “upgrade” button that customers can use to upgrade from a free version of an app to a paid version, or to make purchases from within an app.

Lodsys says that it wants 0.575% of U.S. revenue for any app using its technology.

Apple provides the “in-app billing” infrastructure programmers use to process payments from within their apps, which Lodsys says infringes its patent. In-app billing has been available to iPhone app developers since October 2009, and Apple added support for selling in-app subscriptions to serial content in February 2011.

Not a cease-and-desist letter but rather a warning, the Lodsys letter was meant to encourage developers to “engage in a licensing discussion,” the firm wrote on its blog. However, Lodsys gave the recipients 21 days to comply or else face a lawsuit.

Programmers who said they have received the complaint include James Thomson, creator of the scientific calculator app PCalc; Dave Castelnuovo, creator of the best-selling game Pocket God; and Matt Braun, developer of the popular iPhone kids’ game MASH.

Many apps use Apple’s in-app payment system, so the number of companies to receive the legal threat could soon grow much larger.

James Thomson, developer of the PCalc app, says he has asked Apple’s legal team for help.

Apple did not immediately respond to a request for comment.