When watching older films (by older, I mean before 1970), I always notice the lack of strings in the soundtracks, and when there are strings, they never play quietly. For example, in Mary Poppins, the music is mostly brass and percussion, with strings only occasionally appearing, while Jurassic Park makes extensive use of a cello and french horn motif. Most modern scores (excluding ones composed of pop music or in pop music style) seem to use much more diverse instrumentation than scores from fifty years ago.
I believe strings are typically more difficult to record than brass and recording technology has significantly improved recently (I confirmed this by comparing the B section of the main theme from Star Wars as recorded for Episode IV (1977) and Episode I (1999), the latter having much better string quality).
Has this improvement affected how composers orchestrate their music? Specifically, has it made them more willing to use strings? On a side note, I've noticed the same effect with the french horn. Is this at all related?