hybrid bike running 700c x 40c tires that came with 700x35-43 tubes. I know tube dimensions are very forgiving but have been looking for proper tubes anyway. Found one tube that is 700x28-47 and another that is the same as the original. The 28-47 tube is a $2 cheaper, supports a larger size range of tire and weighs significantly less - 180gr vs 416gr. Am I missing something or is the cheap tire just that?

I am sure the cheaper tube is significantly lighter because of thinner rubber.
FWIW, I use 20-23's for my road bikes as well as touring bikes. Yes it stretches a bit more in the 40 tires but that doesn't bother me.

20-23s in a 40 tire - guess I don't have to worry about tube size in an emergency. will try the cheap tubes and switch back if problems. 35-43s no flats: ridden through glass, off curbs, occasional water filled pothole, dirt paths and nailed a concrete sidewalk slab that was above the path but hidden by grass, very durable so far.