There's much more to it than that. For a start I'd point to the way that supermarkets have been allowed to grow without let or hindrance, and especially the way they've diversified into the book and record markets (among other things), creaming off the profitable mass-market end of the business and making specialist retailers unviable. Then there's a slack planning regime that's simply waved through any number of unnecessary and damaging out-of-town developments, lack of investment in public transport and other things needed to facilitate high-street shopping, crap town planning in the post-war era, and so on and so forth.
IMO any solution to the high street's problems has to start by stripping the main supermarket chains of some of their functions (personally I'd like to see them restricted to being no more than retailers of cheap packaged foods and cleaning products) and preferably breaking the biggest chains up altogether, tightening up the planning rules on out-of-town developments, making the tax system disadvantageous to them, and generally creating a legislative climate in which running an independent town-centre retail business is as easy as possible, whilst initiating a new supermarket or out-of-town shopping centre is slow, difficult and eye-wateringly expensive.
