"By default" here means "in the absence of circumstances requiring some other course of action". So courts base their judgments on the provisions of codes and statutes unless the particular case before them justifies or requires them to base their judgments on something else.

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Note added at 22 mins (2012-02-22 16:19:32 GMT)
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In practice, courts will always base their judgments on the provisions of codes and statutes in any case, but the circumstances of the particular case may shape or modify their application of those provisions. "By default" expresses the idea that there is nothing in the case to cause the court to diverge from a straightforward application of the provisions.