I would go for something like this:Redesigning the site has a physiological effect of new and interesting all over again.
Its the same case where for example apple launches new computer , what for? its not like the old one doesn't work anymore) Well, its not exactly the same with new design ,BUT, it gives you the feeling of renovation, of development,etc etc etc.
i'm all for changing designs, because you always come up with something more interesting and more attractive. So why not change something good for better?I think they just feel like they are redesigning something that people know and trust, and ruing the build up reputation . Well, its not like you change the logo. so its not really important.
Anyway, I would offer to change the design but stay on the same theme.