I'm going to assume you're not asking the question rhetorically (like the FT thread where the original poster insists that all of the airlines flying to/from Japan are horribly price gouging because of his singular data point).

It's not as if the airlines have their executives laughing maniacally as they push a button to raise prices just because they think they can. On most routes which have a competitive marketplace (HKG-LAX qualifies), commercial airlines will use yield management software to try to maximize revenue of their flights, based on historical data and reasonable predictions about what the future holds versus the past. So, given a certain number of seats in the economy cabin on the non-stop and connecting flights that they can use to offer transportation, and that some seats are already actually booked, the yield management software will allocate remaining seats to different fare bases (sometimes known as fare buckets). In your example, at the time you checked initially, the airline may have had 25 seats available for sale at $1174, 3 seats for sale at $900, and 1 seat for sale at $625. Just hours later, somebody buying just 4 seats on the flight will cause the price offered to you to jump from $625 to $1174. Over time, the yield management software will re-evaluate the situation and may make seats available at the cheaper fare bases again in the future.

Then, one relevant factor to consider right now is there's probably a lot of rapid chaotic flight reservation changes being made due to the developing situation in Japan regarding the nuclear reactors impacted by the earthquake/tsunami. Crises like this make the historical data that yield management software depend on nearly useless. I think it's reasonably to believe that by itself (without assigning evil motives to the airlines) can cause some seemingly wild swings in prices. However, overall, supply & demand suggests that the price for travel between the U.S. and South Asia NOT involving connections through Japan could end up going up as consumer demand for the supply of seats that DO connect through Japan wanes.