Actually, it isn't a "line" about the accounting practices. US Sarbanes-Oxley and US GAAP laws require that a company can not recognize the sales of a product until that products is "complete." So, for example, if you buy a car but the dealership doesn't have those tricked out rims you want available for a couple months, the car dealership can't recognize that sale until you get your rims. Blame Enron, et al.
If Apple adds new features now, they could technically get in trouble for already recognizing the revenue for the iPod Touch you bought last year. iPhones don't have that issue because they recognize ongoing revenue due to the model they have with getting revenue still from AT&T.
Is it a stupid law? Yeah. But it's the law.
As for people waiting to get those for "free" - welcome to the high-tech world! I'm guessing you've never bought a computer only to have HP or Dell drop the price by $100 a couple weeks later? Or release a new model in a month that makes yours obsolete? It's the industry... I don't even want to be CLOSE to these boards when Apple finally decides to reduce the prices on the iPod Touch. The teeth gnashing will be heard around the world...