> "why is Google the only company that does something like this?"
Not a company, but last summer the European Space Agency organised the Summer of Code in Space. The homepage (http://sophia.estec.esa.int/socis2011/) seems to be down, but the mailing-list (https://groups.google.com/group/esa-socis) is still up. One important difference with the GSoC is that it's limited to students of European schools.