I wish Stillwaiting! Red Bull posted about this on the prev. page a similar response. I counted something like 13 acceptances logged on the survey page in early Feb, which makes me think that they made all their initial offers at once, expecting a few to turn them down (I think they usually admit 6-8 or something like that). If, say, 8 people turn them down, then they move on down the list.
The way I understand it there are two ways of making offers. One is the aforementioned, the other is for schools that have a "cap" on offers they're allowed to make at once. Say they can only admit 8, they only make 8 offers (ish) and then have to wait for someone to decline to move on. These are the schools that really encourage you to make a decision quickly. There are of course, a number of things that can change the game in both instances and I don't know how funding plays into this. If anyone else can elaborate, please do.
I think the application process is the worst for philosophy students, namely because it's so opaque and we all have a compulsive NEED to know what's going on back there. So we frantically attempt to piece together our impressions of the process. I've pulled mine mostly from a combination of the Splintered Mind, Leiter blog, and some correspondence with DGS's (who are often quite candid about the process via email) so hopefully, it's not just conjecture and has some semblance to the real process.
Friends of mine in other fields simply put their apps in and went skipping through the snow. Since LORs aren't as important in most other fields, they found random instructors/grad students to write them and didn't give it another thought. Come to think of it, everything turned out just fine for them.