IMO it's the Artist who achieves photo realism not the software. True options like radiosity and global illumination make it easier. But even with these options the best tex maps and models it's still the artist who sets them up properly within the lighting. Also getting the little details right, like highlights, refection, refraction, bump to name a few. Personally I didn't see anything in the Terragen Gallery which couldn't have been rendered in Bryce too.

Stephen Ray