[labard1]

You're right that no system can produce perfect fairness, and requiring that standard would produce total paralysis, and thus cannot be taken seriously.

I'm only talking about very big differences.

[free me]

Point taken. But the reality, (as opposed to your original hypothetical), is that most savings accumulated over any period of time are in either tax-deferred accounts, real property or accounts where the earnings are tax free but the contributions are after-tax.

So I don't think many people would complain about the unfairness. On the other hand, if you or anyone else comes up with a way to mitigate it, well so much the better.