My girlfriend is a trained classical singer whereas I'm a self taught musician. She doesn't really gravitate towards the rock music I like to write but because of her training she can easily jam, riff, or write anything far quicker than I can. Songwriting is a very technical skill indeed.
Composers classically trained this way tend (!) to have an easier time writing melodies, harmonies, and progressions in a consistent manner, ie not having to wait for "inspiration to strike". The composer, of course, still needs to develop an emotional connection in the music, but the point is that it can, and routinely is, taught.