Do they simply not have enough confidence in their own flagship smartphone, with an apparently world-beating camera, to show an actual unretouched shot? A great way to crap all over the launch.
Nokia camera's have been good in the past and I have no doubt this is probably a good one.
One ad campaign is short lived, the photos taken by consumers who buy the phone on the other hand will continue to trickle in. It doesn't make too much sense for them to rely on this fact.
What the whole brouhaha is that they probably thought 'It's just an ad, everyone does it, every knows how ice cream in ice cream ads is not real ice cream. And the delicious burger never looks the same in real life either.'
Here's an interesting video from McDonalds on how they make their burgers look great. They admit the shortcomings of a real burger in the looks department and how they make it look so good.