I went from a G5 PowerMac to the i7 iMac, so I'm more than pleased with my upgrade in performance.
Yes it's always good when in the know and to buy just after the release date but I'd hate to buy an iMac after 3 months only to find weeks later Apple has dropped the price. I get your point.
I haven't checked the big name PC makers like Dell and Sony, but in general do their prices remain steady through the models life?
That said I know Microsoft recently dropped the price of Surface mid cycle, with no Surface 2 likely to come soon.
Windows PCs at retail from pretty much any manufacturer drop in price over time and often go on sale or are rebated heavily if they don't sell well enough as there is a lot of competition in that sector. Apple has excellent control over it's supply lines and is the sole manufacturer of (official) Macs and rarely has an excess of product until a product cycle is nearing its end which is about the only time you see any kind of meaningful discounts. This is excellent for Apple's bottom line, but not so good for folks looking to maximize the bang for buck which leaves you with the only method you have left--buying close to release to get as much use out of your full price baby as you can before the value starts to drop when the next model year is released.
All of this of course means nothing if you find yourself in a situation where you need a machine now, in which case you do what you gotta do and maybe take it in the shorts a little bit as far as maximizing value.