The quoted post said "year or two". Even so, I find it hard to believe people are paying 80% of retail for a used machine that is almost out of warranty. Furthermore, if you're actually selling it at a 20-30% loss in less than a year every time, then it's roughly the same as waiting 2 years and selling for 40%.
Either way, I'd love to find the kind of Craigslist idiots paying 80% of retail for a used and out of warranty computer that you can get refurbed as a better deal.
For the record, my 2012 has a proc that's only 1 generation behind the current procs. Those mid-year updates don't really count in my book. The 2013 "update" only changed the next to top end proc from the 3720QM (that I have) to the 3740QM. The Haswell update in 2013 moved up to the 4850HQ followed by the 4870HQ in 2014. The majority of users can't tell the difference in processing power between my 2012 3270QM and the latest 4870HQ. The bigger difference in the used/older machine, IMO, is the battery capacity. Mine is down to 80% of design capacity after ~515 load cycles.
I'm holding out for Skylake because this currently isn't enough difference to warrant me selling my 2012 for ~$1200 and dropping $3k on the latest and greatest:
http://cpuboss.com/cpus/Intel-Core-i7-4870HQ-vs-Intel-Core-i7-3720QM Hopefully Skylake will result in a redesign, better battery life, and better performance. If they delay the release, I may spring for a battery refresh in this machine.