Hi again, Roger -
My main "reference" is an esteemed clinical microbiologist of some 30+ years of experience and education in the field, an author of some nationally recognized studies in the infection control area. I placed the question to him some time back after one of these discussions periodically surfaced on BPL, and at that time he seconded the ideas I relayed in my previous post. I trust the depth and breadth of his knowledge greatly. However, if you have references to the contrary I'd be interested in reading them, and passing them back his way.
My other reference would be any standard medical microbiology textbook. Unless something has changed since I studied the subject, there are two main mechanisms of gastrointestinal illness. One is by the ingestion of enteropathogenic bacteria which colonize the intestines and either produce enterotoxins (normal garden variety E. coli is not one of these, but the enteropathogenic O157:H7 serotype is, as are Salmonella and Vibrio cholerae) or penetrate the intestinal mucosa (Shigella and Campylobacter, for example). The other is to ingest food which has been overgrown with toxin-producing bacteria such as Staphylococcus or Clostridium; in those cases the bacteria don't directly infect the intestinal lining, but the toxins act upon your body in nasty ways.
I can find no reference to any mechanism of normal E. coli acting on the stomach, or causing problems from ingestion (other than the obvious "yuck" factor!).
It may be "simplistic", as you say, to assume that we are not normally consuming small amounts of bacteria on a daily basis, normal E. coli probably being one of the more common as you can find it nearly everywhere if you just set out a Petri dish. That, after all, is how we originally get our gut colonized after birth (from the top down), normally with no ill effects.
However, I am still in favor of vigorous hand washing, make no mistake about it; it is a fine way to avoid spreading disease, introducing pathogenic bacteria from the environment to one's system, or transferring bacteria to food where it may proliferate.