some variables to keep in mind is that, when manufacturers list weight, they usually list the weight of a 52 or 54 cm frame, without pedals, botle cages, and usually with lightweight [latex] tubes. a larger frame will weigh more. period. without pedals [@ 250g], your bike probably comes in at 18.5 lbs. with latex tubes, lighter tires and no additional hardware, it's probably about 18 lbs. for a 105-equipped bike, that's pretty respectable. my 51 cm steel marinoni weighs about 19.5 lbs with pedals.

btw, unless you are a super-fit king of the mountains type, a pound or two either way on the bike will make absolutely no difference to your performance, except psychologically.