It bears repeating: Whether adopted or biological, a child may turn out to be severly disabled physically and/or mentally. This could mean that the parents may need help in caring for that child. It may even mean that the child has to spend great parts of its life in some kind of institution. I don't think that is in dispute here at all.
What happened in this case is something very different, based on the facts that we know. A child was adopted, and then abandoned. Skeptic Ginger, you seem to be saying that perhaps his adoptive family did not know how to ask for help, but they had managed to get through the process of adopting the child, so I find it very hard to believe that they are somehow so very simple that they are not even able to ask for help for that child. Instead, they abandoned the child by putting him on a flight to Russia. Their situation may indeed have been very difficult, but that is till not an acceptable solution.
Families with severly disabled children have my empathy. I have met several such families (adoptive as well as biological), and I do not for one second envy them. But had they done what this family seems to have done, my empathy would have been reserved solely for the child. (And by the way, I don't really think the situation of your friends is at all similar to the one we are discussing, Skeptic Ginger, since I cannot believe that they sent their child alone halfway across the world, to be put in an institution, and never to be seen again.)
What it comes down to is that an adopted child is still your child. You have taken on all the responsibilites of a biological parent, and the fact that you and the child are unfortunate enough to face severe difficulties, does not change this. This may be a drain on all your resources; emotional, financial, physical, but it still does not change that fact.