people that are aware of the new architecture are a minority, forget macrumors and every other apple site.
people that need an apple laptop will buy one regardless of its new architecture or not.
If we talk about 10% less (at max) purchases because customers are holding out for haswell, it will be alot.
what do you think 'back to school' is? a way to get rid off 'overstock'.
Respectfully, all the data pretty much disagree with every word you just said.
Average people don't know "Haswell," but they do recognize other words that matter a lot. Like "new." And "X hours battery life." All of which appear not just on Apple's web site, but in newspapers, Sunday circulars, and so on. And if you think those things don't matter, then I'd suggest you look at Apple's quarterly earnings data by product line for any length of time. You'll find a very predictable sales cycle. In fact, your entire last comment about "overstock" proves my point: that inventory exists only because demand is greatest for new products. Your 10% estimate is, based on the unit sales data, a gross underestimate.
As for BTS, it applies to all product lines. It's existed for several years. Last year's BTS pretty much proves again why I'm right and it's not about "overstock." Do you know what the biggest BTS seller was last summer? The brand-new Retina MacBook Pro. In fact, as you may recall, it took Apple several weeks to even get its supply chain able to keep up with demand; orders placed on or after the day of launch took roughly 2-4 weeks to ship, depending upon configuration.
The purpose of BTS isn't overstock. It's to continue to keep Apple's foothold in the competitive education market and to give students heading to school an additional incentive to not only buy an Apple product, but also to buy it from Apple directly.