Eww... polycarbonate is used by both Samsung and Nokia so your statement is invalid, though Nokia uses quite often a thicker polycarbonate and from time to time they use unibody designs so that increases the perceived solidness. I can tell you that my Lumia 920 feels really premium due to its curved glass, soft to the touch polycarbonate and weight but in hand the iPhone 4 to 5s (haven't used the new 6) feel more premium.
Samsung uses polycarbonate also but in order to battle Apple's super-slim phones it uses a very thin layer of it so they definitely bend with no much pressure. This said, Sammy gives a glossy finish to their smartphones (+ a generic design) and that's why they seem so cheap in hand but probably the Aplha and the Note 4 are the first "premium" Samsung devices ever, lets see how they really feel.
I like what Microsoft did with the 830, giving it a more fresh and premium look when compared to the a-little-dull 930 and I'd rather have an accessible battery instead of a unibody phone any day of they week, it is very frustrating when my 920 freezes and I can't do anything but wait until the battery dies.