What they're trying to convey is you don't want to breath bad air, which is another issue entirely, but you definitely want a house sealed completely so you're not heating and cooling The Great Outdoors (and many of you are given the median year built of our nation's houses is 1974!)

I ran across this concise article in EcoHome Magazine I encourage you to read and share, Debunking Building Science Myths, of which there are many but these are the Golden Oldies. Two of my favorites, "heat rises" (no, hot air rises) and turning things off saves energy (not exactly). 

I'm also particularly fond of this sentence, "Sometimes it is important NOT to let the 'energy tail' wag the 'design dog.'" Amen, people don't build and retrofit homes just to save on utility bills, you have to enjoy living there! (Some of these "eco homes" look like space ships I'd hate to see land in my neighborhood.)

One final point about the house tight versus loose debate, insulation and air sealing work in tandem. Not only must you pick the correct product for the intended application, but you have to install it correctly. One without the other is just a waste of time and money.

So memorize the ideal "build tight, ventilate right". You want a tight house with fresh air from outdoors, not the attic or crawl space, mechanically circulated (and properly filtered) throughout your home.

We also humidify (humidifier added to HVAC system) to automatically put moisture into the air in dryer months so the temperature and humidity remain constant year round and your interior finished space doesn't crack. Remember, this all starts with sealing the house properly with the correct products installed correctly.