"Totally different" is quite vague.What about the issue with the fact that you can get a totally different graph, by starting the counted week on a different day?
In any case, you need a good reason for selecting your start date if you don't want to start at release (which the graph in question does). You could do calendar weeks, but you'd start with one that contains less days than the following ones. Not important in the long run, but less elegant imho than simply counting weeks and starting as soon as you have a full two-weeks period (as the graph shows two week averages).
So, the question is why start with something else than release?