A very practical problem with making data available publicly is privacy. This is likely not going to be an issue for data coming out of the LHSC, but comes into play in CS research. I know a bunch of researchers who work with large datasets that have user locations, cell tower communication, social network data, etc. Of course, even researchers work with data that is annonymized. But almost nothing is truly anonymous. You have to assume that researchers working with the data are going to be sensible about how they use it. If not, they will face serious consequences (i.e. lose their jobs and hurt their reputations). A dataset made public typically cannot be controlled in this manner.

Researchers must also go through IRBs (independent review boards) at their institution prior to engaging in research that deals with human subjects. If the collected data is going to be made available publicly, it makes the process more arduous.

Btw ... there is a decent dataset repository for CS researchers doing mobile computing called Crawdad.