When it comes to battery life, you must consider the affect on the total user experience.
If the iPhone can play video for 10 hours, that means a 2 hour movie brings my battery life to 80%.
If the iPhone could play Flash video for 5 hours and I watch a 2 hour movie, my battery life is reduced to 60%.
Given other things I do with my phone battery life is important beyond "how much video can I watch?" If the repercussions of watching a two-hour video are so much less severe, I am more likely to watch the video in question knowing I won't wind up with a dead phone after a half day of traveling.
If the iPhone can play video for 10 hours, that means a 2 hour movie brings my battery life to 80%.
If the iPhone could play Flash video for 5 hours and I watch a 2 hour movie, my battery life is reduced to 60%.
Given other things I do with my phone battery life is important beyond "how much video can I watch?" If the repercussions of watching a two-hour video are so much less severe, I am more likely to watch the video in question knowing I won't wind up with a dead phone after a half day of traveling.