No surprise there.
Creo/Elements Pro 5.0 has an end of life date of September 2015.
Windchill 10.3 has a release date of Q3 2015.
Why put a dead product with a new one and do all the testing.
Also notice that the actual MR of Creo2 and Creo3 has not been determined yet for Windchill 10.3.