>>4247190JPEGs you get out of the camera (or the ones that serve as a RAW preview image) have been processed by the camera's engine. There are a lot of adjustments and baked-in magic that goes into it.
When you load a DNG into Lightroom you have an unprocessed RAW, using an Adobe color profile (Lightroom doesn't even have any Ricoh color profiles to select either). Adobe defaults tend to be on a neutral side, so things often look a bit flat.
RAWs are for people who are unhappy with what the camera JPEG engine does, and who want to take the time to create the look they're going for. I imagine most people tend to create their own presets for different cameras like I do so that you're not always starting from scratch.