I can only speak for Waterstones and WH Smiths in Southend but compared to Amazon they're overpriced and although the do sell books below the marked price they're generally the ones that aren't selling too well. On Amazon you can usually get new releases in hardback for roughly half price on the day they're released. Waterstones and Smiths often take months before they discount them or have BOGOHF. If it was the odd book every now and then I wouldn't normally be too bothered but when I can save a couple of hundred quid a year by buying from Amazon for me it's a no brainer.
I do browse in the bookshops but mainly only buy from second hand ones. Another thing I like about Amazon is that if you're looking for an out of print book you can post a request and quite often you'll eventually get a copy at a reasonable price.