That will only be this generation the switch. From then on it's two if they elect to cull the HW.
How so ? They've just cut the Core 2 Duos in 2 with this, those using Intel chipsets/integrated GPUs and those using nVidia GPUs.
Next they could simply drop 9400m equipped Macs with 10.9, keeping the 3 year barrier alive. Nothing says they have to cut accross generational boundaries using only the CPU, that's what you think they need to do.