Google appears to be making an advanced and expensive solution to "full" autonomous driving. The limitation will not be in where it can go, but it is initially limited in weather/environmental conditions. The target audience is likely not production cars in the short term, but a system like theirs can for example make their street view photography cars autonomous: they can work in summer, stop if it rains, and it doesn't matter too much if they cost twice as much as a regular car. It will of course be a regulation nightmare to allow the driverless cars out in the street though.
Volvo on the other hand will probably try to make a simpler and much less expensive solution that will have to work in rain/darkness/snow, and not add a significant amount to the cost of the car. Clearly that means having other restrictions, presumably in the overall intelligence or in which roads it works on. Volvo's system is likely intended for making day-to-day travel more secure at the lowest cost possible, not for creating completely autonomous navigation and problem solving (e.g. 4 way stop turn-taking). It must work in almost any environmental conditions, but it will probably require a driver at all times, and will almost certainly not work everywhere.