No, technically whether they or liable or not reverts to normal principles of product liability, rather than their special acceptance of liability.
But manufacturers liability for harms caused by their products, while varying in detail from jurisdiction to jurisdiction, tend to be pretty broad in most of the West (incl. the US, despite it's otherwise weak consumer laws.)
As the default speed limit for such a highway would presumably be 65 mph (and traffic usually much faster), anywhere with such lowered speeds would presumably have special circumstances that would probably make it unsuitable.
The guaranteed 10 second handoff is impressive, however.
From the article:
"[...] Unlike all currently available driver-assist systems, Drive Pilot is designed to give drivers a 10-second warning before switching off; engineers had to make sure that, in every situation, the system would safely and faultlessly hand over control. [...]"
From the article:
"...Handing over driving responsibility completely requires extremely particular circumstances. Right now, Drive Pilot can only engage at speeds under 40 mph (60 km/h in Germany) on limited-access divided highways with no stoplights, roundabouts, or other traffic control systems, and no construction zones. Eligible roads must be mapped by Mercedes for Drive Pilot use (similar to GM SuperCruise); the automaker has already mapped every such highway in Germany, and most of those in Nevada and California. The system will only operate during daytime, in reasonably clear weather, without overhead obstructions. Inclement weather, construction zones, tunnels, and emergency vehicles will all trigger a handover warning. And no, you can't close your eyes or go to sleep while it operates..."