I've looked through the dates on both flights-
LA travelling May 5th and returning May 11th comes out at £341 all inc.
There are other dates available, it's just a case of seeing what suits you
Sales Period: to 30 Apr 09
Travel Period: commencing 27 Feb - 30 Jun or 22 Aug - 30 Nov 09
Hong Kong returns in the first week of May come out at £357 - all dates so far - again, check it out and see what suits you.
Sales Period: to 17 Mar 09
Travel Period: commencing 11 Apr - 21 Jun 09