It's taken a little while, but Apple's flagship music production software and music performance software have arrived on the Mac App Store, joining Apple's other Mac App Store offerings like iWork, iLife and Final Cut Pro.
Logic Pro 9 and MainStage are now available for download from the Mac App Store at US$199.99 and $29.99 respectively. Apple has discontinued the boxed retail versions of Logic Studio and Logic Express (and apparently Sountrack Pro 3, which came bundled with Logic Studio).
Similar to Apple's Final Cut Pro transition to the Mac App Store, this is a dramatic price cut for Logic Pro 9, which was previously bundled with MainStage, Soundtrack Pro 3, WaveBurner 1.6 and Compressor 3.5 as the boxed Logic Studio for $499.
Logic Pro 9 is available from the Mac App Store now as a 413 MB download. An additional 19 GB of optional content is available via in-app download.