I actually question if it was a good idea to make the \score{...}
optional. It may be great for you and me who mostly write short
example files illustrating some feature, since it saves a few
key strokes. However, as soon as you want to typeset some real
music, the saving in time is negligible whereas the risk of added
confusion both to new and experienced users is far from negligible.
You might claim that it doesn't matter for the Regression files, but
I claim that these are a good source of examples for most users and
I fear that it's more difficult for most people to follow even a
short example when you don't see immediately where the (implicit)
\score block is.