I totally agree with the historical argument of making London and Moscow as hard to conquer as possible. If you look at the map, London is sourrounded by neutral Naval Battles, with two neutrals each. So, to take London, one actually has to conquer 2 territories with 5 neutrals on them.
With Moscow, the situation is similar, since it is sourrounded by winter-factor affected regions with a -2 factor each. So, to take Moscow, one must also conquer 2 territories and kill 4 neutrals, but this time during the same move, otherwise one's attack will lose 2 armies at the end of the turn.
As you see, what we wanted to do is to incorporate the difficulty of taking each capital in a more creative way than just stacking a whole lot of neutrals on each of them, and render the difficulty specific to each country''s natural assets: the sea for the UK, winter for Russia.
The question now becomes how much harder do we really want to make the conquest of these capitals, especially for the first time. As Kab said, players will tend to go after each other's armies and the easier to conquer capitals, leaving for later -if at all- the harder ones, like Moscow and London. With London and Moscow neutral for longer, th UK and the Russian empire will be ineffective for longer, leaving a free hand especially to France and the Ottoman Empire. While I think it would be fun to see the Yannisars on the Champs-Elysees or the Imperial Guard in Istanbul, it just wouldn't be the Napoleonic Europe of 1812 any more
I could see the Russian winter territories going up to 2 neutrals each and the Naval Battles around the UK to 3 neutrals each, but I would leave the capitals themselves to 3 neutrals only.