Mitzi: the number of people who contacted TES or LP and said they would be there and the number of people who actually came to help, well you can see how far apart those numbers were. Don't know why people didn't come, some said they thought they would not be needed because so many other people were coming. I don't know where the 'expected number' came from. I know I heard LP talk about it on NG, and I know I heard TM say he was expecting it to be the largest search ever - just don't know where the numbers came from.
I was at the search and worked at the command center both days. Like the people who said they were coming and didn't - Some of the water and food that was promised did not show up either - that I know for a fact. I don't know the logistics of food/water at any other search, I can't answer about what they normally do, I can only tell you what I know about this search. What was incredible though, was the response from local people and non local people when they heard that there was a need for water and food at this search. It made me smile more than once to see a pizza place driver show up and climb out of his/her car with 10 to 15 pizzas and look around trying to figure out exactly 'who' to deliver them to - and the people who showed up with bottled water in their trucks, cars, etc. or placed an order for water and had it delivered.
Hope I answered at least part of your question for you.