Phones and their build materials question

I like to read all I can on all websites about new phones that are out and coming out.

In the comments section of all high end new phones, there are always people arguing over the "premium build quality"

Read an article earlier today that the Galaxy S IV will probably use plastic again. And of course all the comments are Samsung sucks, they need to be more like Sony, HTC, or Nokia, etc.

Looking at each OEM flagship device ( HTC One, Sony Xperia Z, Nokia Lumia 920) I noticed that each of those phones have closed backs for a non-removable battery.

Does anyone think Samsung sticks with plastic so they can have a removable back cover?

Also, is there a phone out there that is glass, aluminum, or soft touch polycarbonate with a removable back cover?

I personally owned a GS3 and having a spare battery is always good to have and had to use it about twice a month.