Incorrect...boiling wort for an hour does infact sterilize. This is one of simplest forms of doing so....anyone thats ever had microbiology in college knows this....surgical implements can also be sterilized in this manor. The most common application of this is in canning, as most gardeners who can their own veggies can tell you. The bacteria must be re colonized into your wort after cooling.....which happens from enviromental conditions (I.e. dust particle in you household air, pollen, suicidal bees, and nose hairs) In practice your wort is almost always re colonized in some form or another post boil.........but it takes time for an infection to grow, and thats when the clock starts to tick. Will your yeast create enough alcohol in time????