Changing the PH of your whole body verses just changing the PH of your mouth are very different. If I drink a fruit juice, that may eventually make my body chemistry rise in PH, but for my mouth the PH will go down while I am drinking it. I could care less what my whole body PH is (unless I have some sort of medical reason for this), but to me if you mix acids and bases in your mouth, it is like mixing baking soda and vinegar = tongue bite. Sizzle, sizzle...
But, also keep in mind that the PH differences in Burleys and Virginias are very small. It's not like we are talking extremes, just "taste-able" differences.
Heck, this is all speculation anyways. PH is just something we can add to our hypothesii and speculations. There are millions of chemical compounds going on in the smoking process. Take perique for example... The process lowers the nicotine levels drastically, as Mark Ryan pointed out to me. He had it tested, and it is by products that are formed that cause the perique sensations of nicotine, or help us absorb the nicotine present in the other leafs of the blend.
Whatever works for one person may not work for another. So, if yours works for you, then great. But, I still get a kick out of watching guys try to drink milk right after smoking, ha ha.