Surely using boiled water is worse than using water straight from the tap? When you boil the kettle, the steam is the bit you'd really like - condense it into a cold container, and you've basically got distilled water. The water left behind in the kettle will have a higher concentration of calcium and others bits 'n' bobs than unboiled tap water.
I suppose using boiled tap water in a soft water area means you'll have killed off most of the bugs in the water, so less likely to get algae etc.
Edit: just re-read the bit about using a water filter to remove calcium etc. Kind of makes sense, although I don't know how effective those water filters are.