I'm simply trying to purchase the computer at the beginning of the design cycle, so that I can maximize the life of the machine. I think that's a sensible move.
There's always going to be better technology/software on the horizon, but that doesn't mean you can't time your purchase properly. Using vehicles as an example, it doesn't always make sense to continually wait for the next model, as they are often announced prior to going on sale (i.e., you'd be waiting indefinitely). However, I wouldn't purchase a 2013 VW Golf because I know the 2014 model is based on a new platform with an improved chassis and more efficient turbocharged motor. This is one example where it does pay to wait and see what happens, even if the current model meets all of my present critera.
I use most of my computers for 5 years or more, so it makes perfect sense to ask these kinds of questions. If I had purchased a white macbook in 2008 instead of waiting for the alumunium unibody, I know I would have regretted that purchase.
You could be waiting a long time. Do you need a computer now?
The Macbooks arent anything like the iPhones where they are re-designed every other year. The rMBP could be considered as a redesign so there is a fairly good chance next one will be in more than 2 years.