it just seems odd that they're offering the white version as the "premium" model, so to speak. for example, the iPod nano- you can get it only in silver in the 4GB version, but to get colors, you have to buy the 8GB model. The black MacBook is more expensive than the white MacBooks. They've always offered black as an option, but at a premium. Now black is the standard, and you can only get white if you get the 16GB model... just seems a bit odd.
But, no, I don't think Apple is trying to say plastic is in, aluminum is out. They've been trying to portray themselves as a "green" company, and aluminum was helping them do that. If anything, going with plastic almost seems like a step backwards in that regard, even though it yields a better overall product since it's supposed to help with signal strength.