I've always been curious about the same....if you read books and watch shows, most clearly say to "rub" the rub into the meat.
My experience has always been that after I sprinkle the rub on, if I try to rub it in, I rub it off.
Rubber gloves with a little oil on them solves that problem.
However, I am very generous when applying rub and leave my rubs on for at least 12 hours before putting the meat to the smoker. I paint whatever I am smoking with exception to fish and jerky with mustard and sprinkle the rub on. That's it. The mustard will moisten the rub and wet it to the meat surface. The vinegar in the mustard will break down some of the tougher sinews on the meat surface.
As far as smoking "drying meat out". I've never heard of masses of people claim that "smoking" dries meat out. Unless you are preserving fish or making jerky I guess. The whole point of BBQ'ing was that poor folks could only buy the tougher cuts of meat....brisket, pork shoulder, all the cuts that are lower on the animal. BBQ'ing - Smoking, not grilling made these cuts tenderize by a low heat and slow cook process. You're taking a piece of meat past well done to the point where connective tissue falls apart.
Living high off the hog, back in the day, meant you had enough money to buy ham. If you were broke and bought a ham, people would say that you're living high on the hog. Isn't it funny now that most people will arrive in masses to good BBQ joint and order those poor cuts. Ever seen a ham joint?