The UK Government have released a response to the online petition to prevent the BBC making the iPlayer Windows only. The government state that the "BBC Trust made it a condition of approval for the BBC's on-demand services that the iPlayer is available to users of a range of operating systems" and they will "measure the BBC's progress on this".
"The BBC Trust made it a condition of approval for the BBC's on-demand services that the iPlayer is available to users of a range of operating systems, and has given a commitment that it will ensure that the BBC meets this demand as soon as possible. They will measure the BBC's progress on this every six months and publish the findings."
http://www.pm.gov.uk/output/Page13090.asp