It's all plastic. If the final product looks the same, what's the difference? Other than one potentially sagging over time due to weight and the other maintaining its shape?
Sorry but this is one of the stupidest statements ever, given the context. I hope you realize that resin and PVC both come in different grades and qualities. The quality used by Sideshow on PVC pieces, like the Man of Steel, is nowhere close to the one used by Bliztway or Hot Toys. So no, you're wrong, it's not "all plastic".There's plastic and plastic. First point.
Second point, I prefer my statue to feel like a statue. Why people make a big deal out of it? Because certain companies... sorry, rephrase: ONE certain company marketed the polystone gimmick in the last decade. I won't tell you which company - take a wild guess. And now the customer base has that kind of preference. We might argue that the weight, the feeling when touching it, like stone, are all accessory and unnecessary to the sight, we might say that there is really no specific relation between these factors and the final quality and the fact that something heavy and stone-y "feels" like quality doesn't imply that it's really quality... but guess what, this hobby is made of a number of things that have little to do with just how good something looks on the shelf. And one of these things is for statues to feel like statues and you can ask anyone, a "statue" in their mind won't be made of super light smooth PVC.
Now, PVC has a ton of advantages of course and it's a better material overall than polystone - this is the rational verdict. Still, for most people, if something CAN be achieved with polystone/resin... they prefer it that way, for the number of reasons just written above.