If one turbo is 'worn' more than the other, then it will present a slightly different resistance to the exhaust flow. It will still drop exactly the same pressure as the other turbo, but flow will be not be identical to the other one. The overall effect will be that combined pressure at the manifold will be slightly lower due to flow being slightly reduced.
In case you understand basic circuit theory, here is the electrical analogy again:
The voltage drop across both of the resistors is always 1.1v. If they are the same resistance then the current will divide equally. If they are different, for example R1 = 1 ohm, R2 = 2 ohm, then twice as much current will flow through R1 than R2. The voltage however, remains the same across both. It can't be different as each side of both resistors is connected together with wire. Just like both turbos are connected together with pipework.
I think everyone else on here agrees that when both turbos come online, the pressure across them is equal. There is nothing to debate, we are just trying to explain it to yourself.