By default, gchart included zero in the response axis, and it is generally the "best practice" to do that.
SAS does provide a way to over-ride the default with an axis statement (but make sure this is really/really/really sure this is what you want to do, and is a good way to display your data, before doing it!)
Remember the cardinal rule about bar charts and axis scales? Because we judge the values in a bar chart by the lengths of the bars, not by the positions of the ends of the bars, the axis scale must include zero. By chopping off the bottoms of the bars, we increase the resolution of the chart, but we distort the apparent values encoded by the bars. I’ll repeat: The value axis of a bar chart must include the value zero.