I agree that graduates do tend to go for the big institutions for employment, but I believe that it is institutionalised advice from Universities, well it was when I graduated and from what I see from the inside still is.
However, there are companies out there taking risks, mainly with grants for funding from the DTI, the EU and what used to be the small business service, including the company I worked for before heading in to a university. Admittedly some of the work never really gets beyond the initial funding, or even out into the open source arena. But like me there are people all over, especially in the HE sector trying to change the system. I do think that is some small way we are winning, as in HE the institutions are seeing open source as a way of adding a feather in their cap. Hence how the project I am working on was allowed to go a head. But again this is only due to a funding stream from the JISC, who have almost made it a requirement to be open source.
Even with these opportunities, as the concept of open source is not really understood by those making the high level decisions in universities in particular, the culture is all wrong. This then affects the sustainability of the projects once the funding has ended. But there are people out there trying to change both the system and the cultures, mainly thanks to the work of Randy Metcalf, and now Ross Gardler, and the lads at OSS-Watch (http://www.oss-watch.ac.uk/). Due to them I no longer feed isolated as they have set up a community which is thriving.
But things are changing just really slowly and more emphasis is being given to entrepreneurship on all courses, so graduates may soon take the risks. Also business in the UK may change if we in the educational sector can show that being part of an open source project can bring credence, a sustainable business model and success.
Anyway rant over, but it really just got my goat. I will put something on my blog about this in hope that more people will debate what can be done to get the UK out of this negativity towards open source.
I will let you know if I hear anything back, but I am not expecting to.