I think that it has to do with how good your imagination is. I always find that whatever I've focusing on is sharp as day, but everything else is a little blurry. Dreams by nature are a little surreal, they are conjured up by your imagination so I would expect that if you are somewhere that you know very well everything will be clearer because your imagination doesn't have to work quite as hard.

I say this from experience, I was in my old house last night (in my dream) and everything was so real I had to actually poke my eyes to make sure that they were still closed. I even asked one of my friends that was there if my eyes were open or closed.