Response to petition to Gordon Brown to resign

Some months ago I signed a petition at "number10.gov.uk" for the Prime Minister, Gordon Brown, to resign. This evening I received an email with his 'response'; just as with Prime Minister's Questions on a Wednnesday at midday, Brown almost never answers the questions he has been asked and he doesn't do any better with his response to the online petition, which has been signed by 72,234 people:

We received a petition asking: "We the undersigned petition the Prime Minister to resign." Details of Petition: "There are many reasons why we might want Brown to resign, but rather than having lots of narrow petitions on this topic (most of which have been rejected), I wanted one for all of us." Read the Government’s response The Prime Minister is completely focussed on restoring the economy, getting people back to work and improving standards in public services. As the Prime Minister has consistently said, he is determined to build a stronger, fairer, better Britain for all.

Why can't he just go!?