The smart ones among us don't.
The Note 3, for example, is available on-line at far, far less than the high street price.
The Galaxy Mega retails at CPW for £440, but you can buy a UK model from Amazon for £289, a massive £151 saving.
Similarly, S4 retails at CPW for £550, at Amazon, a UK model is £397, another £150+ saving.
(I'm talking SIM-free prices here).