Stephane, I appreciate how you like those films so maybe you're right and they're better than I think. Actually I usually don't like to criticize since it is usually more productive to find something good than expose something bad.
On the other hand the conservative aspect of Mozart's writing is because he was a pure Classical composer, not a Romantic, not a Modern. His music was not copied from Italians, but arose out of the Classical symphonic style begun by Stamitz and represented most famously by Haydn and early Beethoven. The short development is also due to the Classical tradition - it was only in the Romantic era of later Beethoven, Brahms, and especially Post Romanticism of Bruckner and Mahler that development became much longer and more complex. An interesting little example of this is how Prokofieff wrote a characteristically "Classical" style symphony, in the 20th century, that featured a short, very tight little development section in the first and last movements that perfectly represented Classical symphonic practice in form though in a modern harmonic idiom.
Also Mozart was not a bad orchestrator. One has to project back into the past - he lived not today when everyone can listen to all eras of music instantly and hear everything that has ever been done in orchestration - but in the Classical era BEFORE Beethoven revolutionized orchestration. Besides, Mozart in his incredibly short life had already begun the revolution that Beethoven took over - if you listen to the later symphonies of Mozart or the Requiem you will hear some powerful, highly perfected and subtle orchestrations.
