I think he changes his accent to make sure he's talking clearly for the audience he'll be broadcast too.
Probably right. Or could just be as simple as having a naturally morphing accent. I've met people like that (and caught myself at times in the past), who have accents that just naturally change depending on who you're around without you doing deliberately.
I'm an Aussie who's been living in the UK since beginning of '05. My accent these days is less Aussie and more Brit due to the workings of time, but whenever I meet other Aussies (especially if there's a pint involved) the broader Aussie accent comes back immediately. In a more embarrassing example, I pick up the Kiwi accent pretty easily if I spend enough time around a NZ native.