Um, that's plain wrong.
Yes, bacteria that thrive in the human body do not tend to live long outside of the body. But there are some hardier bacteria that do live long enough to be a concern, and there are also plenty of viruses that will live quite a while on surfaces.
And do you know germs get onto surfaces? They get deposited from the air. Thus, they start in the air. That happens during flushing.
And ironically enough, the toilet seat is the least filthy thing in the bathroom. Germs get aerosolized during flushing and during volatile explosive diarrhea, and they get stirred up so much that they deposit onto surfaces further away than from the toilet. A toilet seat is hardly the surface you need to worry most about, so disinfecting it is mostly trivial in comparison to other bathroom surfaces.
Also, the purpose of air sanitizing sprays is not to technically disinfect, rather, they neutralize by encapsulating or destroying scent-producing molecules.
Hint: I'm sure you're aware, something being smelly isn't a product of some scientific force like gravity or electromagnetism. Scent is a product of molecules. They can be organic material, gaseous molecules, or root/byproduct chemical molecules. Any particular scent is produced by a molecular cocktail in the air.
So what you smell after a particular rough bathroom trip is a mixture of biological material aerosolized, various odor-producing chemicals, and bacteria or their byproducts. You may not always kill something when spraying the air with a neutralizer, but you are certainly breaking down the molecular cocktail that produces that awful scent. And sometimes, you do kill bacteria or viruses that could live some time outside the body. Norovirus is a particularly hardy germ that can live on surfaces for a long time. A good piece to read about norovirus:
http://www.nbcnews.com/health/norovirus-why-washing-your-hands-isnt-enough-1C8143996
It isn't as simple as "people don't wash their hands" as most people like to imagine when it comes to diseases spread by fecal matter. Washing properly, vigorously for 30 seconds and getting under every surface of nails, is something most people fail to do. Many things might be whisked away in the encapsulated fatty acid bubbles, but some things are hardier than others.
I'm no germaphobe, but it is something to consider.