The 14 tastes different because they use much more sherry cask in the 14 than in 10. I forget the specific ratio, but was able to taste these side-by-side at a recent Arran tasting put on by their brand ambassador.
On related note, they will be distributing an 18 year expression in the next few years. They anticipate including much more bourbon cask aged whisky in the 18 year expression, which should give it some of that spice that is familiar with 10 year.
All told, Arran is making some really good whiskies, and I cannot wait for the 18 year to be released.