If it's anything (it's not, but it's fun to pretend), it could be a sign of integration between the Mac and iOS App Stores. Even if one isn't actually being rolled into each other (which I would assume they wouldn't be unless iTunes was redesigned), it could just be saying "this is also available as a Mac app," possibly with a link to the Mac App Store page.
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As I said in the TechCrunch comments -
If it's anything (it's not, but it's fun to pretend), it could be a sign of integration between the Mac and iOS App Stores. Even if one isn't actually being rolled into each other (which I would assume they wouldn't be unless iTunes was redesigned), it could just be saying "this is also available as a Mac app," possibly with a link to the Mac App Store page.