I'm a little confused here. I have the New Penguin Course and Russian for Beginners by Duff and Makaroff. Duff says that unstressed 'а' after ч and щ is pronounced like и (часы, щадить) and like ы after ж and ш (жакет, шарлатан).

Brown doesn't even mention this. He just talks about 'а' being reduced whenever unstressed. Is this just a difference of dialect? How do Russians from Moscow pronounce it and how do most Russians pronounce it?