Why not say "by the end of 2007?" Well, it's bad business -- Nintendo has three titles (WarioWare: Smooth Moves, Wii Play, and Mario Party 8) coming out between now and March, and then Metroid Prime 3 seeing a release sometime after March. To say Mario Galaxy is coming out before Christmas gives analysts the clue that it might be poised to elevate their holiday lineup, unless Smash Bros Brawl or some heavy-hitting third-party titles can step up to the plate by then.
Past March 2007, we don't yet know Nintendo's first-party lineup. Fils-Aime hints that some announcements will be coming in January. If Nintendo has learned from their follies with the GameCube, then we should have a consistent release schedule for the next year. If not, then we'll probably get one hit game every now and then, followed by long intervals of drought.
[Update 1: It's StePHen Totilo, not SteVen. The change has been made, you can call your snipers off at anytime now.]