I don't know, I think that every generation says this about the "youth" generation of their time. "When I was a lad..."
I think todays youth DO have an amazing imagination and drive- I see so many websites that are brilliantly created by teenagers. The photography & digital art I see coming from our youth captivates me. I see teens with small charitable projects that they developed themselves. A group of my daughters peers (she is only 6) have started up a fund raising group for Heifer international and so far purchased 6 animals. They have had to be creative in figuring out new and effective strategy. It is just a more tech driven or project aimed imagination than I remember having. Different, but not useless by any means.
It is true that our lifestyles (most of ours) are much more sterile now. We spend a lot less time out in nature trudging through streams and trying (unsuccessfully) to catch the little fish swimming through. Or stacking rocks trying to create our own dam of sorts. I do think this is sad for everyone involved- especially kids. So in that sense I really agree that a component of childhood I so fondly remember is fading. It is definitely altering the type of imagination kids today have, but I wouldn't say it is removing it completely.
All that said, my family was primarily media free until all our kids were over two. Now we have a computer but not a TV. We have taken a waldorf approach to their early childhood, and plan to enroll them in school later than societal standard. So obviously I did have concerns about their imagination and the magic of childhood. Oddly though, I am one of those parents who is cautious about who I expose my kids to. I noticed you listed that as a negative or another sample of children not being allowed to be children. For me limiting their exposure to other families who limited media influences and took their kids out to streams and forests in their young years was a choice we made to further their imagination and define a "normal" pattern of behavior.
At the same time, now that they are getting older we do have to blend the world we've created for them with society as it actually exists. So now that my kids are all over two they have access to computers and do enjoy them quite a bit. We also expect them to be self regulating, and don't put a lot of limits on it. We live in a different time for sure, but I'm not sure it is completely draining imagination from our youth. I think there have always been families which have less of an emphasis imagination and families with more of an emphasis on it... but as a whole I still have a lot of faith in the youth of our day and their creative drive.