There's more and more pressure for that kind of thing, but it's still early days in most fields. For an example of a forward-thinking policy, consider the Wellcome Trust: http://www.wellcome.ac.uk/About-us/Policy/Policy-and-positio...
On the technical side of code/data sharing--I think one obstacle (in least in the fields I'm familiar with) is that may researchers put together papers in a way that makes reproducibility needlessly hard. If you do all your stats in something like Stata or SPSS, then paste tables/figures into an MS Word document (which is passed around among colleagues), finding your own errors is hard enough---never mind some third party trying to re-produce your results. If instead, you use tools like Sweave & script the data analysis & paper assembly process (ideally with version control), reproduction/sharing becomes much simpler.