yes... it's a resolution number, not the size of the screen. so, when wow loads, i imagine they do some form of calculation and determine which resolution might be best for the dimensions you choose.

800x600 == 1.333
1024x768 == 1.3333
1600x1200 == 1.333

1280x1024 == 1.25
380x300 == 1.2666 <------

1920X1200 == 1.6

i would imagine if i noodled with the sizes and made something 480 x 300 (1.6) .. it should remain 1920x1200 resolution... but i wonder if wow jumps to 800x600 for the size, at which point, wow's aspect ratio calculation would be off (i'm at work.. i cannot check... if someone else could, that'd be interesting)