I can't speak for everyone, but our (meaning my company's) pricing is set based upon our expenses, profit margins, etc. The tax credit is something offered directly to consumers by the government and has no bearing whatsoever on pricing. The only way I'd see anybody's pricing going down is if consumer demand falls off a cliff. All indications are that this will not be the case.
+1 I agree. Prices didn't go up when the tax credit became available. Pricing on windows by profitable companies don't shift when consumer incentives like tax credits come along. Pricing is based on the cost of doing business. Consumers were buying windows before there were tax credits, they will be buying them after they are gone. If anything, window prices may rise if demand drops off and manufacturers reduce their supply.