I honestly don't know - I do notice that among the adoptees I know, the ones who came out of orphanages or foster seem "more" satisfied than the ones who were direct placements.
It's also good to remember that whenever you're reading on a forum, people are here because they have an interest in the topic. There are likely hundreds of thousands of adoptees who have never given their adoptions more than a passing thought - you're not likely to find too many of them here.
Also keep in mind that most of the adoptees you hear from were adopted in the 70's or earlier. The way adoptions were conducted then, versus now, is like comparing apples and asparagus - they both start with a, and that's as far as similarities go.
We won't really be able to determine if international adoptees are "more" content than domestic for probably another 30 years - it's a relatively new trend, all things considered.
Focus on being the best parent you can, loving your child as much as you can and being as honest with them as you can. That's what defines a "successful" adoption - not whether or not a child grows up curious about where they came from. Curious doesn't equal unsuccessful.
