Judging by comments by our Canadian members, as well as material presented in "Holmes on Homes," it appears that our northern neighbors have been much more persnickety about sealing boxes and protecting the vapor barrier than we are.
I confess to paying little heed to the vapor barrier in my work. I also routinely see many penetrations of the barrier by household electrical.
In my 1957 house, the electrician preserved the vapor barrier by running the wires atop it, just under the face of the drywall. Mind you, this was before the NEC had any nail plate or setback requirements for Romex.
We certainly saw the results of hasty sealing after the Carter-era "energy crisis." The trapped moisture directly led to the 80's "mold" panic.
Tighter houses have also led to many changes in the mechanical and plumbing codes. Simply put, everything that burns gas or vents air really ought to have a specific supply of fresh air- whether it be a water heater or bath fan.
IMO, we're still barking up the wrong tree when it comes to moisture management. You simply can't seal all of it out, forever. You can, however, give it a way 'ou