I disagree. a) other companies announce ahead of time and they seem to do ok and b) a lot of people look would at what's coming and say it's not worth the wait and buy now. Besides, as you said " The vast majority of the population buys when they need something" so they wouldn't even bother to research what is coming.
a. Apple isn't like other companies
b. Nobody outside MR knows what the flip Haswell is.
They don't have to research if you're obviously announcing/advertising it.