Cheong wonders why there isn't a way for the Maximize button to maximize a window across multiple monitors. (Troll asks a similar question: Why doesn't Windows support spanned mode for multiple monitors?)
We tried it that way at first. And we quickly discovered why it was a bad idea.
Wait, I'm not finished yet. Things get still worse if your two monitors are not the same size. In that case, the virtual screen is larger than the visible region. For example, my monitor arrangement has a landscape monitor on the left and a portrait monitor on the right, with the bottoms of the monitors aligned.
If a window were maximized across the virtual screen, the contents of the upper left corner would not be visible at all!
Now, there may be specific cases where it would be meaningful to maximize a window across the virtual monitor, and if a program wants to do that, it can certainly implement that on its own. But even for a picture-viewing application, maximizing across the virtual monitor may not be a great idea: Pictures often have people in the center, and then you end up with somebody's head cut in half.