Listerine, floss, brush, repeat.
Ok, maybe not the repeat part... =)
I've wondered about the idea that flossing might introduce bacteria to the bloodstream as well but I think it's a matter of how severe the bleeding is. Unless your gums are REALLY bad (in which case you're probably not flossing anyways) there shouldn't be enough bleeding to allow bacteria where it shouldn't be, however a dental cleaning (or other proceedure) is a protracted affair which may inflict some real "injury" to the gumline and elsewhere and I think that's why the prophylaxis is neccesary.
Of course the other problem is, if you're flossing every time you brush and you take amoxicillin (or whatever) when you brush because of that, the bacteria amoxicillin is supposed to protect against will mutate to a form that's unaffected by the antibiotic.
Antibiotics are prescribed WAAAYYY too much these days and there are mild forms of antibiotics in all kinds of things now like soaps and hand creams and baby wipes and dishwasher detergent and and and....
I cringe at the thought of all those bacteria these products are supposed to protect us against developing immunities to all the antibiotics we have....