A typical Carnauba wax will protect from 4-8 weeks, depending on environmental conditions, exposure, etc. A good polymer sealant will last 3-6 months, again taking the above variables into consideration.
In harsh weather conditions, I'd use something like Meguiar's NXT, Meguiar's #20 or #21, Klasse Sealant Glaze or Zaino every 3 months and any Carnauba monthly. And make sure you apply a very thin coat. If the product hazes up white and thick so that you can hardly see the paint under it, you have put it on WAY too heavy!
As far as NuFinish - if I remember right, didn't their commercials refer to it as "the once a year car polish"? If so, and if they are using the terminology correctly, then it is a polish, not a wax. Polish is used to correct paint defects and prep the surface to be waxed. This is the step, or series of steps, that really gives you the shine. The wax or sealant is what protects the finish, and imparts some extra gloss or alters the shine/gloss/reflectivity of the prepped paint.
Water beading is not necessarily a sign of a protected, waxed surface. Some sealants will actually cause the water to sheet more than bead, and yet the paint is still "protected". I just washed one of my cars with Dawn and then clayed it. I gave it a quick wash to remove the "residue" of the clay/lube process prior to polishing, and the water still showed a good amount of beading, yet I guarantee you that after a Dawn wash and clay, there was no wax whatsover on the surface of my car.