Anyone who buys a Macbook Pro today, before they're updated in the fall, will be able to use it for the next 3 years without issue. My Macbook Air was purchased in 2012 and is still fast enough that I probably won't replace it for another 2 years. People keep their computers longer now because they're fast enough. This has been true for the PC industry for at least 5 years now and it's why sales have been declining since they peaked in 2011 [1]. The year over year changes from Intel/AMD are incremental and I suspect Apple has decided they're not going to buy every iteration. It's even less important to get every chip now that Intel has stretched their development cycle from Tick-Tock to Process-Architecture-Optimization [2].
[1] http://static1.businessinsider.com/image/56968e64c08a80492c8...
[2] http://www.anandtech.com/show/10183/intels-tick-tock-seeming...