The article makes some fine, if obvious, points.
The big one is housing, no mortgage makes a big difference in retirement needs although doesn't apply to renters.
So many people I know (family members and older friends) refi'd in the 2000s, either for cash out or for lower rates. They won't have paid off houses by the time they hit retirement age.
It used to be a thing to steadily pay off your mortgage for 30 years (and then a burn your mortgage party). With all the refinancing going on, that's much less common nowadays. And that's IF you didn't move at all in the previous 30 years, from age [edit: 35]-65. Heh, sure.
It does happen, of course. Some people get 15 year mortgages. Some people pay extra principal. But it's more rare than common, I'd think, and assuming a paid off mortgage in retirement is a big stretch, IMO.