What is the purpose of the §/± key on a UK Mac keyboard? This question is just for curiosity.
My UK Macbook Pro's keyboard has a key in the very top left with the symbols § and ±. (On a US keyboard the ~/` key is in this position.) From looking at pictures of the newest Macbook Pros, it seems this key has finally been phased out, but I'm still curious about the reason for its existence up to now.
Let me say at the outset, I'm looking for answers based on specific known facts about the reason for the key's inclusion, which probably means either some insider insight into Apple's decision making, or at least some knowledge of the history behind it. A lot of answers so far are based on opinions or speculations, and it would be greatly appreciated if that could be avoided.
The symbols on the key, § and ±, seem quite obscure and rarely used. § is an old-fashioned symbol for a section heading in a document, and is still used in the printing industry, while ± is used to quantify errors in scientific and engineering documents, as well as in high-school maths (i.e. the quadratic formula). But even in those specialised contexts the choice seems odd: why include a special key for the section marker § but not the much more common paragraph marker ¶? Similarly, why ± and not ≈, Δ or √?
It seems odd to have a dedicated key for these relatively obscure symbols, especially since it doesn't appear on the Apple US keyboard layout, or on a non-Apple UK keyboard.
So basically I'm just curious about the reason for this key's existence. It seems unlikely that British Mac users have a special reason to use these symbols often, so I would guess the reasons for including it were either historical or technical in nature, or possibly they had to do with one particular Apple employee's personal preference. But what, specifically, were those reasons?
As noted above, I'm looking for answers with specific insight or evidence about the decision-making at Apple regarding the existence of this particular key.
I think only Apple knows the answer to this.  

The § and ± characters are available on the US keyboard at option 6 and option-shift =.

I believe a historical antecedent for the ± key can be found in the IBM Selectric 3 keyboard.

Other Apple hardware keyboards with the same key in the same place are Arabic, Bulgarian, Czech, Dutch, English International, Greek, Hebrew, Portuguese, Romanian, Russian, and Turkish.  I suspect their users also wonder why Apple gave these two characters such status.

A much bigger mystery in my view is why the Apple British keyboard puts the " and @ characters at different places than any normal British keyboard does.  Apple eventually had to provide a "British PC" option in system preferences/keyboard/input sources to accommodate all the folks who are used to the British standard.