The 25 exemplars say otherwise. They're about process re-engineering, technology modernisation and legacy integration. And they're also nowhere near complete (only 9 are live[1]).
People have been complaining that some legacy documents and manuals weren't available on the new gov.uk site. So now they've started bringing them over, updating them to work in modern browsers and on touch devices, so in this context their only spec was to make that content available on the new site.
In the larger context, yes, they've been doing some actual redevelopment. But how do you re-develop a HMRC manual? Heck up until a few years ago it was only available as a PDF(!). Even the old site was a marked improvement, and this one just keeps that document pleasantly available for the future.