I think Angus/Malcolm are getting older, which does have some impact on the band along with other band member changes. The band completely changed after Bon Scott died, yanno. It is really hard to get a new lead for a band without making compromises. Most bands try to find a clone of the lost lead singer, which can be good and bad. I would rather see AD/DC stick to their signature sound than to come up with something new and creative though.