I did not know about Aero Snap when I posted the question. I had only seen the behavior on the top because I realized the mouse pointer has to reach the edge of the display before it activates and the only time I reached that point was when moving the window up.
Chappy posted a keyboard shortcut for maximizing vertical. Win+shift+up arrow, so I will probably use that. The Win+ right or left or up or down arrows also work well. But it doesn't work if the Aero Snap is turned off.
System Manufacturer/Model Number Homebuilt OS Windows 7 x64 CPU i7-2600K Motherboard Asus P8Z77-v Pro Memory 8 G Graphics Card GTX 480 Sound Card Onboard Monitor(s) Displays LG W2753V Screen Resolution 1920x1080