This is most likely because the hosted service applies a special treatment for urban areas that is not (and cannot easily be) included in the open source engine: Difference between open source car and graphhopper maps car
One of our goals is to get rid of this discrepancy and hopefully this pull request https://github.com/graphhopper/graphhopper/pull/2637 will make this possible. You could already try this branch to slow down the speed in the city center. And if you do please do not hesitate to share your results here 