This all sounds plausible and very correct. I'm with Cathan though on the "boom". Time for Mythbusters.
Thanks for all the input, and after hearing the "20ft from vertical pipe" thing that sounds correct to me. After reading that, I checked a sink drain in my basement that is at least 15' from a vertical pipe, and it appears there is some sort of Studor vent on there. Not sure if it still functions, or is correct, but it looks like they attempted something similar when it was installed.
I'll have to bug a plumber and get the skinny.
Sorry for the thread Hijack! Now back to the missing ladder....