I beg to differ – I don’t know how it’s done or what tag is used to control it, but somehow the wordpress default theme “resizes” images that are wider than the text column. Maybe it’s taking the inefficient route of resizing in the browser by passing the width= parameter inside the img tag?
When I use the default theme with my blog (daverea.com) it shows the images cleanly the same width as the text column. Using other themes, if the image’s pixel dimensions are wider than the text column, the image spills underneath the menus on the right side.
So it is possible, we just need to figure out how it’s done.