I think it was like this. Medvedev being in Shanghai was reported about the morning Luzhkov's statement that he is not going to resign voluntarily. And Dmitry Anatolievich, without hesitation, gave the command to run the decree, which, of course, had already been signed ahead of time.
Nevertheless, it is still an important question of political management:

1. Guaranteeing the loyalty of courts in case of Luzhkovs appealing the decree about his resignation.

2. Reinforcement solutions texture of the power structures and, if necessary, to rapidly start a criminal case on the mayor and his entourage.

3. Securing the loyalty of Moscow Duma.

4. Interception Luzhkovs media resource.

5. The possibility of blocking the financial resources of Baturina (since the main money abroad, West help will be needed).

6. Explanation for the resignation to the Moscow voters.

7. Correction of the regional election campaigns (10 October - next local elections) remembering this image blow to “United Russia”/”Edinaya Rossia”.

8. Strategy of the Moscow development and its binding to the electoral strategy for 2011-2012. Perhaps, simultaneous elections in Duma and in MSD.

9. The positioning of the new leadership in Moscow. Creating the city system of checks and balances.

And by the way, last but not least, why not going back to the idea of "Big Moscow" with the boundary of "Betonka”? That would be the best way to solve the transport problem. But then the most important is to create a city government system of checks and balances (the "Moscow tandem, possibly increasing the Moscow City Duma and local government), for the sole ruler of this monster, whoever he was not to be too influential.