Why the App Store Preview In iTunes?

This is not a “How do I” question, but it is something that’s been bugging me for a while. Maybe someone will have an answer to this question.
When on a website that has some app available in the Mac App Store, there is usually a link that says “Buy in the App Store” or “Download in the App Store”. You would think that this link would take you directly to the Mac App Store. But no, you end up on an “App Store Preview” in Itunes where you can’t really do anything but click on the “View in Mac App Store” button. Why this intermediate step? Why not just go directly to App Store?
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JC Blanchard