I work in such an organisation, albeit a rather small one (~ 60 people). It is absolutely not easy: some people are not cut out for it and would prefer a strict specification and focus on writing the best code, which clashes sometimes with delivering quick-'n-dirty customer value. Other people are just not that good in recognizing the patterns in businesses. I think our end result is better than that of most companies, but at the same time it is much more difficult to manage properly, so I can see why so few organisation take such an integrated approach.