The Democrats give each precinct a number of delegates, no matter how many people actually show up to caucus. This is a representative system: many people, one vote.
I thought it was funny that the party names seemed exactly opposite for the Iowa caucuses.
I learned this from David Freddoso on the Corner where he summarized it this way:
Republicans around the state are meeting tonight to have a large, statewide straw poll, just like a primary. You could think of it as one big caucus. The importance of each precinct, as in normal elections, will be determined by how many people turn out overall. Although the Republican vote on candidates is totally non-binding, it is the result we'll all be talking about tonight — for practical purposes, it is all that matters (unless we go to a brokered convention, and then it's hopelessly complicated anyway).
On the Democratic side, it is different. Each precinct awards a preset number of candidate delegates proportionally. It doesn't matter whether 100 or 1,000 people show up from your precinct — all that matters is the proportional vote in each individual precinct. The party reports the estimated delegate count to the media — not the number of votes. Each Democratic precinct, then, is a separate battle tonight, with no real relation to the others. If six people show up to a precinct that selects ten delegates, then those six voters have the same power as 600 voters who show up in a precinct of similar population.