Linegraphs
The first column of data is taken as the X-values. This has the same effect as passing one less column and setting the X-values with the Versus property. The default is to assume that all columns of data represent sets of Y-values to be plotted against (1..n) as timeseries.

ch.Set 'style' 'xyplot'

Cloud charts (3D scatter)
In this case, the first 2 columns are taken as the X and Y values. Columns from 3 onwards are taken as independent data series, giving Z values. This allows you to call Cloud charts passing a single 3-element array of arrays rather that using the Versus and YVar properties to set the values on the X and Y axes.