The article is discussing zoning codes; not building codes. Different issues entirely.
It's not uncommon to find that you'll need to retrofit an old building to match current fire safety laws, etc. My family recently had to rip out a bunch of old electrical outlets and replace them with newer ones that were deemed safer.
As long as you can get a Certificate of Occupancy (which in my town requires smoke and CO alarms only), I'd never cure a building code violation in a building I was selling (certainly not in the current Cambridge/Somerville market).
You want the code violation cured? No problem; I'll take one of the other 17 offers.
It's not uncommon to find that you'll need to retrofit an old building to match current fire safety laws, etc. My family recently had to rip out a bunch of old electrical outlets and replace them with newer ones that were deemed safer.
Nobody requires you to match current zoning laws.