Ya, my theory holds for negative sums too -- I'd rather have a chance of not losing [large amount of money] than lose [almost as large amount of money] for sure. A $900 loss could be enough to bankrupt me -- I need to take the 10% chance.
The problem with that question, to me, is that the 10% difference in outcome is nearly inconsequential. By the time I'm losing (or gaining) $900, what's another $100? If the proportions were different, I think the question would be more interesting.