I think it is a good thing that it is made of plastic. If it was aluminium it would weigh more, but the biggest problem would be dents.
Have a look at beolab 7.1/2/4/6. they useually all have some kind of dents in them.
Aluminum full of small holes will bend or dent easily. Of course it would look better, but only until it is dropped once.
And the joke of the day about aluminium:
"The Irish are trying to be American, that's all it is. Everything American does Ireland has to do as well. Next thing you know, the Irish are going to start saying 'aluminum', and that'll be the last straw as far as I'm concerned. If that happens, I'm not going back! Everyone's got their own reasons to dislike Americans, 'aluminum' is top of my fucking list, ladies and gentleman. Aluminum cans, aluminum – what the ***'s aluminum foil? Honestly! Everyone knows it's pronounced 'tin'!"
-Ed Byrne