Does magic change the world

I was reading around about GURPS and found
http://ravenswing59.blogspot.co.uk/2013/09/ggf-3.html
and
http://ravenswing59.blogspot.co.uk/2013/09/magic-as-technology-take-ii.html
which postulate that on the whole magic does not change society, because maths.

But I think their math is wrong.

Take their example magic item that would change the world: Purify Water.
( Read more... )

Basically, if you can get enough mages in one place to even teach each other a broad enough range of spells to make an Enchanter, and if those Enchanters understand the value of working together, and if they feel like making money on a regular basis through making simple enchanted items, then magic will change the world. Even the simplest items could make pure water for all of London in a few days. Even one Purify Water item could make clean water for a whole medieval sized town. And be made in an hour.

The only way for magic to not change the world is to mess with mages: make them too scarce, uncommunicative, uncooperative, or too unlikely to become Enchanters. If the basic GURPS assumptions for magic can be met, then Enchanted items will pile up and nudge the effective tech level upwards, starting a demographic upward spiral that puts more mages into the system.

Of course if demons are a serious and regular problem, you can also get a mage downward spiral, or outright crash. See 'too scarce'.

But OP's math is just peculiar, for someone who says they're using GURPS, and I disagree with their conclusions.