The one with the trees probably isn't photoshopped -- I've seen old cabins in Alaska with trees growing on the roof -- we have a picture of my grandfather sitting on one such roof, spotting for moose on a hunting trip.
photoshopped no, but the roof looks like it is having trouble with the weight.... there may be some question as to occupancy. If it was me, I would not be letting trees grow on my head. Of course, how long can you let them grow before pulling them out does more damage than leaving them alone?
That cabin doesn't look occupied -- I don't think that the ones I've seen in Alaska with trees on top were occupied, either (I know the one in the picture with my grandfather wasn't). Any house requires some maintenance -- having a sod roof would require keeping the tree seedlings pulled out! Unless you build a really sturdy frame and have deep soil up there.
Of course, in the far north, trees don't generally get very big.
I have spent time in Norway and can vouch for the grass roofs there. I would guess only 1-2% of the buildings I saw had grass roofs but when compared to the amount I have seen in the US it seemed like they were everywhere.
None of the roofs I saw had trees or even bushes on them, so I imagine the trees in the photo are a result of a maintenance issue. I also noticed almost all the grass roofs were on barn type structures and not very many houses.
Every time I saw one of these roofs, I would remember all the hoopla back in the states about this new crazy concept. Clearly, people have been comfortable with this concept for hundreds of years, why try to reinvent the wheel?
Bradon, I would imagine that the reason most of the sod roofs you saw were on barns rather than houses was that those roofs were built prior to good waterproofing membranes being available. It may be somewhat acceptable to have a minor leak in a barn roof (although not good for the structure in the long run), but it's not so great to have one in your house.