This may be particular to the field of biology, but I find biology talks to be much more interesting than papers. One contributing factor is that important papers in Science and Nature are subject to stringent length limitations. This limits the writer's ability to unfurl a coherent narrative. Oftentimes, years of research are condensed into a handful of figures and sentences that cannot convey the more subtle points of the argument (for that the reader is directed to the supplementary information, which is often many times longer than the actual paper).

On a more macroscopic scale, talks also allow scientists to highlight deeper themes that are often lost in the minutiae of a technical paper. This is especially important in biology because we want to find universal paradigms from experiments done on model organisms. A talented speaker can distill the most important themes from a body of research in a way that writing rarely achieves.

In summary, talks are a great medium for conveying conceptual narratives. In biology talks, the important assertions are almost always backed up by a slide that shows real data. However, if I am an expert in a particular subfield and really want to get into the details, of course I'll go read the paper.