I don't think this is the work of MediaWales - I think its an official render from Foster and Co, with some labels added by MediaWales.
I think we are forgetting the purpose of these kinds of renders. They are in effect, marketing images. So they show bright sunshine, beautiful sunrises and beautiful people. I recall the old Bay Pointe ones having fireworks going off in the night sky - as if thats a regular occurance in Cardiff! So, they add little details to make the place look more bustling or attactive - trees, people. If that is in the area outside the area of development, they clearly don't pay as much attention to detail.
I think that the "low rise glass office buiding" is part of the official indicative masterplan, as well. You can see it on this plan:
http://planning.cardiff.gov.uk/online-a ... 627711.pdf. Not sure why you think its infeasible to build.