Needless to say, developers once burned have now tightened up the contracts. Buyers must realize that developers get their financing on the basis of pre-sales and rightfully expect and deserve all pre-sales in their development to complete.
So, the pre-sale game changed. But probably for the better.
Builders offer the 'pre-sale discount' because they're trading return for security; they need to sell-through on the units they're building. If a bunch of the pre-sell buyers then flake-out and decide not to pay, the builders are in a hole.
The point that I'm making is that this has no effect on the trajectory of prices; its merely a small discount on the market price for those units. Pretending that this is a key driver of prevailing market prices doesn't help anyone; if the market wasn't already rising feverishly then 'shadow-flipping' and 'pre-sale flipping' would carry more risk and you'd lose money as often as you made it.