A lot of cyclists are obsessed with weight. Typically one person's first assessment of a bike will be to lift it to see how much it weighs, as though it is some kind of metric to its worth or function. I find this somewhat amusing and misleading, almost a bit naive in some aspects. Weight does matter, well if you are doing a lot of climbing or are going to be lifting the bike up stairs or manhandling it a lot. I myself tend to be the type that weighs most of the individual components during a bike build, for example when I built my Cinelli Xperience which weighs a respectable 8.2kg. However this hides the fact that when setup for actual riding with lights, computer, water bottles, spares and tools it weighs more like nearly 10kg. I can see the point of being obsessed with weight when you are doing long distances, lots of hills and/or actual racing, however most people don't actually do this very often.
Where it becomes somewhat pointless is when (lack of) weight is used as the primary factor for assessing bikes when it's somewhat unimportant: utility or town bikes. From my own experience building and fiddling with many kinds of bikes, I have a reasonable idea of typical bike weights with regard to type and function. Weight only really becomes a synonym for performance or quality when talking about racing/road bikes: 6kg for the high-end machines and 11kg for the heavier low-end machine.
It seems absurd to start to use weight as an assessor for bikes that are meant to carry things (this is code for bikes that are for practical use). The further you get away from racing the more absurd it becomes, however what is truly absurd is when comparisons are made between racing bikes and utility bikes. People will often lift town bikes and comment on how heavy they are compared to a race bike, however it's like assessing a 2 tonne van by commenting on how fast it accelerates compared to an open wheel sports car, rather than assessing it's capability to help you move house. A lot of people in the Anglophonic world have forgotten about the usefulness of the bicycle as a tool for transport and can only really see it from a narrow racing-oriented perspective. This is particularly a shame as the English have a rich history going back to the early 20th century of producing some of the world's best transport and utility bikes; I find it ironic that what we now call Dutch bikes are really what was once known as the ubiquitous English 3-speed.
How much does weight actually matter when climbing a hill though? I've always maintained that an extra 5kg makes no difference when you are hauling 15kg of shopping on your bike. I've used the climbing calculator at http://bikecalculator.com/tripMetric.html to determine the difference weight actually makes on a typical 6km commute with 2 hills, flats and some headwinds.
10kg skinny tyres, drop bars for different riding positions, no cargo capacity, mudguards & exposed drivetrain.
16m59s, average speed 21.21km/h
20kg, fatter tyres, upright riding position, mudguards, cargo capacity and enclosed drivetrain:
19m8s at an average of 18.81km/h.
Town bike minus 10kg (hypothetical)
10kg, fatter tyres, upright riding position, mudguards, cargo capacity and enclosed drivetrain:
18m36s at an average of 19.35km/h.
This gives you a difference of 2m10s which is about 11% or so, which is a significant difference. However let's actually see what is causing this difference. If you had a hypothetical town bike that was exactly the same except the weight was halved to 10kg you would get 18m36s instead of 19m8s. This means halving the weight only saves you 32s, or about 3% faster. From this you can deduce that the main reason the race bike is 2m10s faster is due to the better aerodynamics and less rolling resistance; less than 1/4 of this 2m10s difference is due to just weight.
This study does not really reflect real world factors however. It becomes apparent that though that the 20kg bike is probably something like my Raleigh Superbe and the 10kg bike is like my Cinelli Xperience. The Raleigh is able to pick up lots of groceries on the way home, doesn't make my clothes dirty, requires very little maintenance, is comfortable on crap roads and is very durable. It however is slower mostly due to the less aerodynamic position and less so due to the weight. The Cinelli is fast, handles beautifully on smooth blacktop, however is somewhat delicate, high maintenance/cleaning and can't really carry anything on the bike other than tools and a spare tube.
It should be apparent that to save 2m10s every trip you have to give up a lot of convenience and time spent maintaining, charging lights, cleaning clothes and fixing flats. It also means you have to give up being able to pick up very much shopping or cargo and will have to spend time going back to the supermarket to do so.
In conclusion, judging a bike by its weight is mostly pointless unless you are planning on riding up several alps mountain passes and/or are going to be lifting it a lot. It just makes assessing a town bike by its weight even more absurd. If you want to go fast, focus on aerodynamics - forget about weight because it's not important for the vast majority of riding people do. Which leads me to conclude that something like a touring bike is excellent if you want speed and cargo capacity and don't mind the higher maintenance and riding position compared to a town bike. Leave the race bikes for the enthusiasts that get up early and ride in bunches.