You got it wrong. People don't think that Zelda could see a delay because of Metroid, people think that because Zelda won't be ready for a release in this year, Nintendo needed to delay Metroid in order to have a big game in the second half of the year. Delaying one game, because another isn't ready isn't a behavior that's unlike Nintendo.
Though, the other important thing that you dont take into account: People feared that Zelda could slip out of 2010 because the OP said that the new date of Metroid is "TBD". "TBD" didn't sound promising at all, especially since it seems like Metroid is already quite finished.
Now that we know the date of Metroid, it really shouldn't affect Zelda. But we didn't know this some days ago :3