I know that it can't change, but as you say, it's used in two locations. So defining it once and then cross-referencing the constant means that we don't duplicate the string literal. 

In addition, when it comes to pulling out strings to be translated, having these kind of strings as literals make for a more difficult job in figuring out magic strings (like this) vs human-readable text (which needs to be translated).

FWIW Eclipse can put // $NON-NLS-1$ markers on the line (or similar) to indicate that it's a non-translatable string, but I thought we'd see this string more than once.