They are not the same and they don't even try to achieve the same purposes, Grindhouse is a pastiche. You know, there are different tones for movies. Just because he made Grindhouse, you think he can't adjust himself to another project he's working on? especially when he's not the director, but a producer who's in charge to supervise the thing.
Predators won't be like Planet terror because it doesn't suit. Oh, and Planet Terror is great fun.