The blacks, brightness, and contrast aren't a matter of exposure. They're adjustments to the tone curves. A neutral curve represents the data in a flat way. This is true to the pixel sensor data from the camera, but looks lifeless and dull to the human eye.

So, a more interesting curve is set to produce a higher black level and more contrast. This reduces some of the data in the image from the pure neutral form, but it looks a lot better. Selecting the curves that look the way you want them to is one of the essential functions of RAW conversion (in addition to demosaicing and sharpening).

Many cameras have settings for different "picture styles" in the camera. That's how you select the different curves you want for in-camera conversion from the sensor to JPEG.

With film, the different tone curves are inherent to the type of film, and are affected somewhat by development choices. Being able to make this decision after the fact — or even in-the-fact but with flexibility shot-to-shot — is one reason people like to work with digital.

I don't know ACR, but it appears that the defaults are selected to produce something that looks more appealing than a flat, neutral RAW file as a starting point. This makes sense, as otherwise you'd have one million newbies complaining that the product sucks and produces awful-looking images without a lot of work. It's my understanding that you can tune the ACR defaults to your liking.