Is dry rub necessary in making bbq ribs?
Your ribs will have a lot less flavor if you do not use a dry rub.  However you can minimize some of the time (and only a bit of the flavor) by putting on the rub, wrapping in foil, and immediately putting them in the oven or on the grill.  The process of putting your rub together probably takes only about 5 minutes - it's the fridge time that takes a while.

Sitting in the fridge allows some of the flavors to permeate, and if you used a more permeable material could allow your ribs to air out a bit.  These are good things, but for my rib recipe I don't put the ribs in the fridge and they still taste great.  I also don't put the barbecue sauce on until about the last 20 minutes of oven time, when the foil comes off and the sauce goes on.  Until then the ribs stay in the foil.

I looked up North Carolina (which uses a sauce that isn't tomato based in the eastern part of the state), South Carolina (a mustard sauce), Texas, Memphis (which uses no sauce), Kansas City (tomato based-sauce that is rather sweet) - all of them used a dry rub even with wide variations on the sauce and for both beef and pork ribs.