[waegawegawe]

I think what you mean is, "why do so many high end laptops have thin, metal, unibody chassis?"

But, when you ask the question that way, it kind of answers itself. People like metal, because it feels more high end than plastic. Unibody chassis don't need to be fastened together, which is good for manufacturing and looks. People like thin laptops because they are more portable than thick ones.

[jrs95]

Unibody helps make it thinner, too. A traditional laptop design had to have both structrual components and outer casing -- unibody designs do both and save space

[freeone3000]

It's technically not unibody, the keyboard (and its GPU) detach.

[linarism]

You may also find that the unibody MB has the screen portion housed in a different aluminum block than the body. Semantics are dumb.