Although I found the price decreasing by 90% at each change somewhat distracting. 2TB of data costs only 10% more to store than 1TB? People with less than a terabyte are subsidising the big boys.

It's more like storage isn't the driving factor of the costs. At low end, you'll have some fixed per-user costs; as you go from mid to high end, you may enjoy some economies of scale yourself, and you may want to pass some of those savings on to your customers.

If you look at Google One, they actually charge more for each increment on a per-GB basis for the first few increments.

A linear discount would be more fun.