Yes, I'm very curious about this, so I'll be interested to hear what you find. I guess it makes sense that there were more photographers and press at the finish line, so people were already filming and just continued after the bombing, but there had to be plenty of cameras around the second bombing as well. Maybe people were more reluctant to hang around in case there were more bombs that were going to go off? I wondered about medical personnel getting to that second site too--as most of the medical people were probably grouped near the finish line, I would assume. There are a number of reports from experienced medical people talking about how many lives were saved by the quick action of so many to stop people from bleeding out and to be able to give IVs so quickly to keep fluid levels up, etc. It probably kept some of those people from going into shock and saved their lives.
I just have had the impression that there were more serious injuries at the first site, but that may not be a correct impression. I wondered if there was something different about the placement or effect of the second bomb, or possibly the people weren't grouped as closely there?