I find particularly audiences now have grown up expecting something to happen. After all that time, his admiration is undiminished. There is a formula for making cadenzas but the content is different every time. Bob talked about everything and spoke in French and German - he's a polymath. While in Australia, Levin will show audiences the art of extemporising, a normal expectation in Mozart's time but rarely seen now.
Few musicians have the confidence.
He will not only make up a cadenza for the piano concerto, but also ask for tunes from his audiences from which he will improvise a substantial piece in the exact style of Mozart. A surprising number of people would like to offer a tune up, but have no means of knowing whether their tune is remotely Mozartian and they don't know how to write it down. Out of an audience of 1000 we usually get back 40 or 50 themes. They get put in a bucket and Bob selects the first four in style. While he loves his music, Hogwood also loves hearing no music at all.