I have had a lot of real ale in England and I don't think they are all using highly mineral-rich water, either.
Not all English waters are highly mineralized. There are areas with Pilsen quality water. I think some of the reason for the recommendations that Charles pointed out, was that the brewery water treatment firm he cited also sells products that will end up mineralizing the water with high SO4 and Cl. Their AMS product is a mixture of hydrochloric and sulfuric acids and that can result in high SO4 and Cl levels when neutralizing high alkalinity. Their recommendations are probably skewed by that reality.
I appreciate someone piping up with that opinion. When I brought this up on one of the English homebrewing forums I sometimes visit, I was severely lambasted as an unknowing Yank...unfamiliar with their tradition. As Skyler points out, any of us can test out high mineralization at any time. Most of us have found that more modest levels do tend to create better beer.
PS: Try dosing minerals in the glass first. That will help you find your desired mineralization without wasting a batch.