I was at a friends tonight who moved here from England and he was commenting that cider here was sweeter than cider in Britain. Do all the yeasts make a dry cider that is back sweetened or do some yeasts finish drier than others?
I agree with mtnrockhopper regarding using yeast to affect residual sweetness in cider. As far as what your English friend said, I might guess he was referring to what some cider producers may do to their product to make it more appealing to a wide audience, like back sweetening.
The naturally occurring sugars in apple juice are very simple and are completely consumed by yeast during fermentation. This results in a naturally dry-tasting product. Many people prefer a sweeter product. The problem with adding sugar to achieve that sweetness is that if the yeast are still present and alive, they will ferment out whatever sugar you add and the cider will be dryer still.
You can add unfermentable sugars, like lactose, as I do, but if your consumer is one of the 60% of adults that is lactose intolerant, they will not be thanking you.
Most people who back sweeten either filter or pasteurize, and then add either sugar or apple juice to raise the sweetness.