First to answer your question. People care about him leaving CCBB because we think he has done an excellent job in the role, and we have high hopes that if and when Chitty goes to Broadway he will be in the driver's seat.

A great many people feel strongly that Chitty the stage musical was a wonderful adaptation of the film. It is a musical that is great fun to watch and full of exciting moments, i.e. seeing the car flying above the stage.
If you have read the entire message thread, you will see that the discussion has gone beyond his leaving Chitty in London to discuss what else he has done. Have you seen the 10th Anniversary concert of Les Miz? Michael Ball was Marius. He originated the role of Alex in Aspects of Love in London and again on Broadway. He was also Giorgio in Stephen Sondheim's Passion when it played in London. He can also be seen in the ALW Birthday celebration, singing Gethsemane, All I Ask of You with Sarah Brightman, Gates of Heaven, and Love Changes Everything (his signature song).
But while he excels in singing show tunes, he has expanded his repertoire beyond them-- he sings love songs, rock and roll, inspirational, -- he's even done opera. He is a man who puts his heart and soul in each song he sings, no matter what the genre. He is a singer well worth listening to.