Direct manipulation of data points on charts Excel 2003: You can drag data points on a chart and change their source values on the worksheet. Excel 2007: Dragging data points to change the source values on the worksheet is no longer supported.
Source of information: http://office.microsoft.com/en-za/excel-help/excel-97-2003-features-that-are-not-supported-in-office-excel-2007-HA010198895.aspx#BMcharting
And what does this have to do with Libreoffice?
So to have a correct explanation of this feature request: The idea is to be able to allow modifying the value of data point directly in the chart. I see several problems on the way to this feature. The current design with data providers and data source hides the relationship between data point and data. Additionally this is a bit of a nightmare when ti comes to cells that are the result of a calculation and not pure values. I suspect that the Excel team removed this feature for the second reason. We would have the least problems with the internal data provider but I suspect nearly nobody is using the internal data provider as long as the chart has not been copied.