Well, I think the PF article was entirely too breezy & without hard facts...But I too don't heat as much as is often "recommended" for some fish. There's a lot of temp fluctuation over the course of a day & season to season. & yes, fish do tend to live longer at their lower rather than higher temp range.
But, unlike Tiff, I don't see my breath in winter either here in NorCal or in Mass. My winter sleep temp is & was 62*F, day 68*F...but higher in summer of course. But filtration & any powerhead-type devices also raise tank temp & tank water mass keeps it from dropping very fast, even in a 10g RCS tank, IME. Lighting raises that even more during "daytime". So, yes, I believe most fish can handle some temp range daily & seasonally...a drop can often bring on breeding too. I need native natural temps ranges over time to even begin to make sense of this issue.