...how many hours I can expect to run 720p video full screen for on a single charge? This is on a 13" 2010 macbook pro.
That's not true. Apple doesn't claim 10 hours for watching video:According to apple, 10 hours.
This should answer most, if not all, of your battery questions:The wireless productivity test measures battery life by wirelessly browsing various websites and editing text in a word processor document with display brightness set to the middle setting.
If you're watching DVD's or downloaded video, realistically you should expect a good 4 1/2 - 5 hours
I can confirm this estimation. Just turn off anything you'll not need, like keyboard backlight, bluetooth, wifi, put screen backlight to a reasonable value and you can get around 5 hours.
Tested playing MKVs using VLC.
Good luck.