Raw is usually used in a workflow that includes post processing. Jpegs can be post processed in the camera. I guess features like Canon's Picture Styles sort of do the same with raw. I think that most people shooting raw + jpeg are either needing immediate jpeg proofs plus raw files for post processing later, or they are hoping the jpegs will work fine, but want the raw files for back up in case a photo needs major tweaking. I haven't used CS3, but I've heard they have incorporated many feature for editing jpegs that were previously only available in raw software.
I shoot raw 99.9% of the time, because I love post processing (even for family snaps). I only only shoot jpeg when I need the photos pretty close to finished straight out of the camera, or I'm low on memory.
I find correcting wb in raw processing software to be very easy. Wb only changes when the lighting changes. Most of the time I am shooting dozens or even hundreds of photos in the same lighting, so I can batch process the wb of all of them in seconds. On the other hand, I can understand how someone else might want to do a custom wb on the scene at the exposure. Even if it only takes a minute (getting out the gray card is what would take me the most time) to do a custom wb every time the lighting changes while I'm shooting a wedding it would add up over the day, and I usually find that I'm scrambling for time as it is. I often can't afford the time when I'm shooting, but I have time to spare later. In a tricky lighting situation where I have plenty of time I do occasionally set a custom wb.
Often I just set my DSLRs' wb to 5000 degrees, like they were loaded with daylight balanced film (I find Canon to run a little warm, for other brands daylight might be 5200ish). Back in the day shooting color film, unless I was willing to do expensive, and time consuming testing I was stuck with either daylight or tungsten wb.