Even in a bi wire system there is some kind of xover network. If it is only a two way sytem it may just be a simple high pass filter, but the reason the tweeter does not get fried has nothing to do with paths of least resistance but but rather the fact that there is some kind of circuitry between the full range output of the amp and the intput terminals of the tweeter that is limiting the frequency content of the signal to only those high frequencies that the tweeter is designed to handle. Or in the alturnative you can use an active xover and bi amo the speaker, but then again the amp that is feeding the tweeter would be badwidth limit at the input. The function of a xover network is to act as a traffic cop and make sure that each frequency is directed to the driverr that is designed to reproduce it. The reason the bass notes don't fry the tweeter is because they never get to the tweeter.
Keep in mind, I am not saying that there are not sonic differences between the two wiring configuration, just that your speculation as to what causes those differences are not correct from an engineering perspective