The Letter of the Law and the Spirit
A storyline is building in the Democratic primary of two kinds of leadership, more or less: the hard worker verses the prophet. The line tends to continue... this is what the worker has accomplished, but the prophet just talked.
But let's run the line in a slightly different way. My lait understand of a major difference in British and US law is that the US loves the letter of the law. The clarity that this activity is governed by that regulation, and here are the things you can do and this is what you for forbidden. The British conversely say these are principles we have to govern our actions, how we want it to work, but let's not get into details until we have a specific case with details.
In the US we see often see the negative implications in things like three-strikes, or the regulatory differences between regular and investment banks, or hedge funds and derivatives. More recently there was the TSA stomping on the civil rights of the poor woman with the nipple piercings. I'd argue that you also nurture a legal personality that parses words to build in loop holes, as we see with HRC. Sometimes the burden of keeping all that parsing clear becomes too difficult.
The problem with conflating the letter of the law as the best means to attain the spirit is that the letter is of the law is merely a means of measurement, but not a true representation of what is. "What is" takes context, descretion, consideration of impact, things that seem soft with out context, but crucial in the heart of any difficult problem.
Obama on the otherhand, while not being so detailed in the interest or tax rates, carries a heavy burden to deliver principles. Principles aren't so vulnerable to context. Principles see the effects of the details and realizes that the means of enforcement need to change (where the three strikes, the TSA fair particularly poorly).