But what the government failed to mention (judging by what you've told us about the article) is that the atomic blast generates such a massive quanitity of heat and energy - that the radiation it causes is actually secondary.
The pressure wave comes first. Then the heat and fire.
The massive change in pressure caused by the explosion is what's knocking down the buildings, blowing out all the windows, etc.
If you are in a building within say, 2km of the initial blast radius - chances are you are toasted long before the radiation will have any effect (along with any building you happened to be in). This is assuming the bomb is of the magnitude 12 to 22 kilotons of TNT (Fatman and Little Boy).
I forget the exact distance, but there were people pretty close to where the bombs in Japan actually exploded and they were okay (well, okay insofar as surviving the blast itself) because they were in the right place at the right time (underground tunnels and stuff). Of course, direct hits are designed to take out whatever is that they hit, but that ends up being a much smaller area than you would think. And we're assuming that the nuclear blast is done a direct surface strike. Over an area that isn't heavily fortified (for example, a city), an atmospheric detonation would be better because it can affect a much greater area instead of making sure one small spot is destroyed really, really well.
And the technology used in these warheads is now vastly outdated. There exists very little documentation on what the current nuclear capabilities of warheads are, all that exists is whether or not certain countries possess the means to create nuclear arsenals.
Not much has changed and there isn't much need for better bombs. You'll be doing more damage with ten 20-megaton bombs than one 200-megaton bomb. Once the bombs get big enough, it does change into quantity over quality.
Edit: Minimoose makes a good point that dirt is most likely to be your best bet. I had a lecture as part of a History of Science course I did. One module was about the Atomic Bomb. We were shown a poster in which the public were advised to wear 'wide brimmed hats to shield their eyes from the light-blast', and 'to hide in a freshly ploughed furrow in a field to escape oncoming radiation'.
Dirt is good because it's cheap and easily accessible, depending on where you live. I don't really have access to sheets of metal and tons of bricks and concrete, but I can dig out my front yard.
It's right that the light will reach you before anything else, but if you can see it, you're probably not in a good place. (expect that window to be in your face shortly after if you're in a car or building)
As for escaping radiation, that advice is terrible. Radiation does damage over time in an area. It's not something that you hide in a ditch from so it passes you over and then you're okay. Though you might want to jump in that ditch for other reasons, such as protecting yourself from the blast and whatever's flying around in it.