My view is (and this is purely personal - I don't particularly like Brown - a flawed - very flawed - genius) is that Brown only offered AV and STV in 2010 because he wanted to stay in power.
Back in this ATL's 2007, from what the OP has in the timeline, Brown wants to go it alone. He'll do that to the bitter end, because his majority is more than just 4. As already mentioend, it's probably 14 at the moment in actuality.
Come the next election (assuming it will be 2012) Brown will be toast, blamed for everything by everyone. The Labour party won't be able to form anything as the Conservatives will likely win an outright majority, and if Labour manage a few more car crashes, they could well see themselves returning only 1997 Conservative level of MPs (circa 170).
I never viewed Labour's offer of AV or STV or any other form of election reform as anything more than opportunistic. They had thirteen years, and majorities of 179, 166 and 66 to push reform through and they didn't.
That's not to say the Conservatives wouldn't introduce AV either. They won't. But at least they tell you straight they don't want anything other than FPTP.