For more insight into why the sites are the size that they are, please see this section.
We address the question of why “the sites are so big” as part of our Help section, because we get it a lot. Yes, you tech savvy wizards of the intertubes running panoramic flat screens at 1680+ pixels across (which happens to be my screen resolution) may be shocked to hear that there are still many many people using monitors set to screen resolutions of 1024 x 768 and below.
So, please consult the holy grail of the intertubes, the great and powerful, all-knowing Wikipedia. Here is a link to Wikipedia's article on screen resolution, where it is stated in a little chart that about 14% of “Internet Users” are still viewing the web with monitors at 1024 x 768. Shocking, we know. :)