You are not wrong that dice ‘bend to their combined median’ when rolling multiple dice and adding them together! But with percentile dice, we are not adding the results, so the combined median model does not apply.
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There is no actual difference between rolling a 'd100' or rolling '2d10 with one tens die and one ones die', this goes for any dice, digital or real.
There IS a difference between rolling 1d12 vs 2d6, vs 3d4. This is because there are multiple ways to roll some results when using more that one die. Craps is a dice game built around '7' being the most common roll on 2d6.
Once you use a d10 for the tens place and a d10 for the ones place, this property no longer applies; there is only one combination of dice rolls that result in each number 1-100.
2d50 WOULD give the kind of center-skewed result you are describing, but of course then you couldn't roll a '1'!