In fact, they can and do prevent the search engines customers' buying sponsored listings. In this respect, SEOs are a commercial risk for a search engine.
Peter, with all due respect, that is incorrect. Look, I think your analogy to a bar is wrong. A better anaology for a Search Engine, although quite still poor, is a TV station.
I feel that assumption is misplaced because it doesn't make good business sense as far as the SEs are concerned. Why give free drinks at the door when you make your money over the bar?
Television stations sell Advertising. However, the product they offer is television shows. Has any television station ever said "We need to get rid of shows. They just get in the way of the ads"?
No, because without viewers, the ads are worth didly squat. And Google is living proof of the power of a model that promotes giving away free drinks, in your analogy, or programmes in mine. If dropping free resukts is a good business model, then why does Overture.com get so few visitors directly? The simple fact is that the Search Engine's business model is based upon visits. More visits == more revenue. Google, who by all accounts is the most successful SE, has decide that maximising visitors is far more important that maximising revenue per visitor. And their growth has, and will, continue to grow at a rate above general growth of the internet as a whole.
So, assumming an SE has to give away some clicks for free, and that this is the best Strategy to increase market share, the question then becomes: do SEOs add value to Google, and other SE, or not? Only they can decide that, and Google in particular has been hostile in the past. Doesn't mean Google believes that SEO is 100% bad for their index or any of the other stretches that often get bandied about.
I love debates about definitions and if this is yours lotso, then I have to agree 100% with you. Unfortunately, however, your definition isn't what the majority of people take SEO to mean. by trying to argue your own definition of a word, you are arguing a self fulfilling prophesy. "I define the word to mean what best fits my argument, therefore I am right".
IMO Making your site accessible to spiders is not SEO. Usability is not SEO. Marketing is not SEO. Even clean code is not SEO.