science and expectations in SF

Betsy's comment yesterday makes me want to revisit this issue...

Re. science: One of the authors in my critique group recently wrote an SF story that prompted a lot of discussion. The gist of the discussion was this:

1. Science in SF doesn't have to be correct, but
   
2. it does have to be internally consistent.

I have thought about this quite a bit and IMHO virtually NO science in SF is correct. Many of the classic elements of the SF paradigm are wrong. For example, as far as we know there are no such things as intelligent extraterrestrials but if there were, they couldn't visit us because there's no such thing as faster-than-light travel.
So, basically anything goes except contradicting yourself. However...

Re. expectations: According to convention, one thing that differentiates SF from fantasy is SF authors are supposed to explain the events/whatever using 'scientific' terms. In fantasy, the whatever-events are not explained other than to invoke the concept of 'magic'.

Authors are free to write whatever they like as far as I'm concerned. Nonetheless, reader (and editor!) expectations can impact the success of such a story. In particular, if the protagonist of a story is a scientist, one expects some scientific explanations. How did the wormhole portal open up? How is the alien traveling back in time? How is the electrically-neutral particle being affected by electromagnetic fields? How do we have negative absolute temperatures?

The "hows" are the science, but the "whys" are the plot. We need those, too. :)