Isn't it essentially the same thing, but less formal

0.1111... is just a notation for (x + x^2 + x^3 + x^4 + ...) with x = 1/10

1/9 = 0.1111... is a direct application of the x/(1-x) formula

The sum of 0.0111... + 0.00111... ... = 0.012345... part is the same as the "(x + 2 x^2 + 3 x^3 + ...) = (x + x^2 + x^3 + x^4 + ...) + (x^2 + x^3 + x^4 + x^5 + ...)" part (but divided by 10)

And 1/81 = 1/9 * 1/9 ... part is the x/(1-x)^2 result