The Executive Branch has a lot of control over how laws are implemented. No matter how well- or clearly-written a bill is (and they are rarely either), rules have to be promulgated based on the law and there is a whole, long process between the passage of a bill and the implementation of that bill, during which there is a whole lot of room for interpretation.
However. The use of signing statements to guide that implementation as a regular step has not only ended, Bush's signing statements are being undermined as much as is possible.
(What? You thought I would just be throwing up baby pictures and videos forever? Sometimes my brain still works.)