I haven't paid much attention to the actual advertising, but my understanding is that splenda has the same molecular structure as natural sugar, with the exception that some of the carbon atoms are replaced by chlorine atoms, thus making it undigestable. Frankly, I don't care how they market it, so long as it behaves in the body the way they say it does.
I like Splenda myself. . . but have to limit my use of it.
I'm one of that 5% or so who can tolerate SOME Splenda, but after a certain amount, it results in massive gas and diarrhea. It even says so on the box. Guess I just got unlucky, and am sticking to Aspartame. . .