Agreed, whether they will insure you should depend on whether you've made a claim in the last x number of years (which they also ask you), not how many years "no-claims" you've had. That should purely reduce the quote by x percentage each year. Doesn't work like that for some reason though.
Anyone ever tried getting a quote off one of the companies that advertise 75% reduction for 5 years no claims, first stating you have no no claims, then remembering you do and requesting a 75% reduction of the initial quote? Bet the first quote isn't 4 times higher on most cars (may not apply to Supes).