The recently publish data from UNPAN shows us that the differences are practically absent. In the following image, I have plotted the correlation between the E-Government measurements and E-participation measurements.
A straight diagonal line, which is clearly visible in the plot, means that there is a strong correlation. I.e. that the E-participation measure can be extracted from (or calculated from) the E-Government measure. If the data looks chaotic, which is not the case here, it means the measures from E-participation and E-Government are independent.
This plot clearly shows a strong correlation. It even has a Pearson Correlation, which is a statistical way of showing that to data sets are correlated, is a staggering 0.66, which is extremely much in the social sciences.
The question which naturally arises is why bother with both measurements?