I think I found the problem.
Since I only wanted the the "Datepicker" widgets I unchecked everything and just selected that to download. Usually when you deselect all and pick the components you wanted it will select any other required one.
It seems to me that the 1.8rc3 released requires additional component (I don't know which) where as 1.7.2 does not.
I was able to get the datepicker to work when I download all 30 components.