The field of web/graphic design is one of those exceptioned to not needing a certificate, degree or diploma. Like Ethan and many others, they probably had a large insterest in this field since when they were young and imagination carries through their work. My I.T teacher has discuss this in my class and there is a difference now between a person who has certificate and high grades and another person with no real certiciates but has done a considerable amount of work for clients. I would probably think that companies would go for those having experince with clients already and its not neccessarily they would take the other one. If your going to college/university its more about the theory side of design. In Australia here, we have Tafe (Techinical and Further Education). Its a bit different than Univeristy or College because in terms of academic marks and grades, marks and percentages are lower. It doesnt mean that students that go here are low-grading students, Tafe takes a different perpective and allows students to grab a larger hands-on approach and more work you do is practical and thus allowing you much experience. Paul (Soulty) has gone to Tafe and he certainly liked it 
You dont really need a Bachelor Degree in this field. If you got what it takes, effort, high interest and a good sense of creativity and imagination, than nothing else takes place of it. But when you increase your work and knowledge well thats when its approariate to work for a diploma I guess, to boost considering clients confident in your work.