I think it looks better with shadows for the columns - when you are playing with realism there are some things, like superheros that fly or fish that talk that are cool and there are others like two similar objects one with a shadow and one without that simply irritate the eye. It's also a question of the artistic medium you have chosen. The overall impression is photorealism - so anything that obviously contradicts that is going to look wrong. It's a beautiful scene and the closer the lighting gets to real the more enjoying it is to look at.
Another point is that in the photo you posted as an example there was in fact a great deal less contrast - so much so that you could see the frames between the individual window panes and the variation of light as well as trees outside the window.
I have to disagree with Babyduck on this one because I think in fact the photo demonstrates precisely the point and photos are the place to start looking if you want to create photorealistic scenes.
So specifically I'd bring the lighting down a touch on the windows - it feels like we should see at least a little detail in the panes - also the shadows directly behind the columns would be a lot darker because the light wouldn't be so diffuse from the surroundings to light it by bouncing back - just opinions to take or leave
btw. nice work - is this part of a larger project or are you doing just this one scene?
Check out the subsurfacescattering on my tongue...