I completely agree that string interpolation is often superior to a format string, but it's important to note that they are not equivalent. String interpolation is generally evaluated in-situ and has full access to the local scope. Format strings on the other hand can be passed around and manipulated (even at compile-time) and can only ever access the data they're formatted with. strftime and strptime are a good example of a format string usage that can't be replaced by string interpolation in python.
D also has the capability of implementing string interpolation using mixins - though the resulting code isn't quite as neat.
