There's quite a few manufacturers that have this technology other than Mercedes
The more advanced "self-driving" systems are all Mercedes-Benz technology that is part of their high-end vehicles (and not a standard option). Remember, Mercedes-Benz holds over 80,000 patents on this stuff and more coming all the time. There's no doubt they are pioneers in vehicle safety systems including self-driving cars.
Edit: Mercedes-Benz actually omitted quite a few even more advanced "self-driving" features from their new S-Class since, even though the technology was ready, regulatory requirements and drivers themselves were not ready for pure self-driving vehicles. (Taken from an intervew with Marc Andreessen on the new technologies in the S-Class).
Additionally they have automatic parking.
Missing from this is only the driver alertness detection.
EDIT: relevant link http://www.volvocars.com/uk/explore/pages/innovation-areas.a...
Often they develop these things in conjunction with a supplier like Bosch. They then get a period of exclusivity and then Bosch/whoever are free to sell the systems to other companies.
That's why you can look at an S-Class and figure out what's going to be in an ordinary car in 10 years time. ABS, Airbags, pre-tensioners, stability control, adaptive cruise-control - not all were MB inventions or even debuted on an S-Class, but all have been features of an S-Class long before everything else.