You are right, ducks4you, I should not have said "never" because sometimes the seed is just fine. I should have said "often." I read that from a guy who used to buy seed for a seed company. And I'm sure it varies by seed company too.
My main point is they sell the best seed to farmers because farmers buy in larger quantities and know bad seed better than home gardeners. So, if you as a home gardener have a bad experience, it isn't always your fault, it could very well be bad seed.
Yes, the seed you save should be better adapted to the conditions of your own garden.
ETA: The seed I described above that I had saved, I also shared with a member here and she said hers were thriving well too . . . in a much different climate than mine. So I don't think my seed was particularly adapted to my climate (only been growing it for two generations).