Modern agricultural planting and harvesting equipment is already GPS guided, this is more of an incremental step to full automation of something that was probably 80--90% there already.
Which is, realistically, the stage Google is at now. The car seems to be able to drive just fine until an outlier condition arises.
What makes the Kinze system interesting is that they must feel confident enough about the safety/obstacle avoidance features to ready it for mass consumption. Again, the complexity of monitoring a field is not to the level of the road, but it does show that a lot of progress is happening in the study.
It does show promise for Google to be able to pull it off on the road too.
