Zelda can easily break 2m first week. Twilight Princess was 1.1mil between the GC and Wii versions. If the game turns out well, I can't see it not being a big hit, and Zelda is probably as frontloaded as it gets, anyway.
As for releasing all three within a small window, why not? Metroid Other M is actually not a very big game (it won't move hardware, and its sales won't be high), while SMG2 is merely a sequel to a game already released this gen. If we see a hardware bump, it won't be big. Zelda Wii, on the other hand, is the first Zelda truly built up for the Wii, so this is more important.
People seem to be in disbelief as these are all highly anticipated core Nintendo games, however this is generally how their releases operate. Look back to the bombs dropped earlier in the gen - in the U.S., we got Mario Galaxy in Nov, Smash Bros in March, Mario Kart in April, and Wii Fit in May. In America, all of these were the best sellers of their time, only eventually topped in sales by the other trifecta late 2009, of WSR in July, WF+ and NSMBWii in November.
The first round was definitely bigger for hardware pushers, though - within 6 months, we saw the first 3D Mario, Smash, Mario Kart, and Wii Fit. This will probably never be topped.
It's time for another. My guess?
Metroid Other M: July
Super Mario Galaxy 2: September (room for Zelda)
Wii Vitality Sensor: Oct-November
Zelda Wii: November (required time to finish the game)
It just may happen... this round more set on capturing the traditional core.
