I managed to count 20 shuttles that survived to the frame before the fade towards the title part. With 800 people to sort between them, does anyone think 40 people per shuttle is a stretch (or somewhere close to that number in case Pike was rounding up etc.), especially if not every shuttle was packed, like the medical one, or do you reckon that those shuttles are spacious enough to hold 40 each?
Think about it this way: "Ensign; get in the shuttle with those other 39 people and live or stay here and die."
I believe there was a thread a few weeks ago on this very topic.