The original delineation of the Scottish whisky producing regions was based more so on tax than style. England did step on the industry somewhat and felt it justified to tax different regions at different rates, with volume and output coming secondary (tax-wise) to location.
Speyside has historically been considered a Highland Whisky, at the time when there were but four official regions that had been identified – Highland, Lowland (only three remain), Campbeltown (which had also been removed and re-included as an official region before) and Islay.
Given that Speyside is home to the greatest concentration of distilleries in Scotland, it then was decreed that it deserved its own status as a region. Thus…Speyside IS a Highland Malt and a Speyside Malt at the same time. Most will identify (when speaking in more broad terms) that they have a preference for a Highland Whisky (i.e. Oban or Dalmore) vs a Speyside Whisky (Balvenie or Macallan). They both qualify as Highland, yet are distinctly different in terms of geography and flavour profile.
Also, Islay is a stand-alone region in itself, while other island whiskies do not have this distinction. Sky, Jura, Mull, Arran and Orkney will identify themselves as being from a specific island but there is no formal “Island” designation.
To further confuse the issue, many consumers are “blinded” by the arbitrary geography of it and believe that region dictates flavour profile. To have it said – not all Islay Whiskies are big, peaty monsters and accordingly not all Speyside Whiskies are fruity and fun. Bunnahabhain 12 YO is very lighly peated while Curiositas from BenRiach is a phenolic bomb.
Hmm…now to some fun stuff…
They had a good thing going with The Macallan. All of the proprietary bottlings were matured (not finished) in Spanish Sherry Oak Casks. But, they decided to expand a bit and offer a different expression of The Macallan and launched the Fine Oak Series in 2004 to high praise from the global whisky reviewers. Jim Murray for example awarded it “Best New Scotch Brand” when it was launched, and others have agreed. They are as different as two expressions could be, and consumers have a distinct choice to make when asking for a Macallan. And hey – they are welcome J
I know this is likely more answer than you had anticipated but I am of the mind that no information is useless. I have also enclosed some more electronically for your perusal.