Absolutely. Not to be an ass about it, but Amsterdam is flat as a pancake and San Francisco (which he compares it with) is definitively not.
Bikes are often very practical in cities but not when it's raining and not when the gradients are significant. Despite the rain and minor inclines I have a Brompton http://www.brompton.co.uk/ here in London and adore it.
Denmark is at least as crazy about biking as Amsterdam. In Copenhagen it's a major advantage to be on bicycle, specially in rush hour where you easily get from A to B 2-3-4 times faster than cars.
Rain is not really a factor, Copenhagen is rainy all the fucking time. Steep roads definitely is. But it isn't all. In Buenos Aires, which is relatively flat, I saw maybe 3-4 bikes in as many weeks. The major factor, IMO, is presence of bicycle paths and the fact that bicycles are actually a part of the design of the 'traffic flow', which means that bikers are first class citizen in Danish cities, while I would never even fuckin' dare to ride a bike in Buenos Aires - it's simply not safe.
Automobile ownership happens to be discouraged in Denmark. Naturally, people bicycle in a nation in which it is essentially illegal to own a car. http://www.google.com/search?q=denmark+car+tax
Ok, there is a 180% tax on cars. 15k Honda fit = 42,000$ (ouch), but that just makes the used car market more valuable. I had a working old Volvo that was worth ~1k and needed 1-2k of work done per year to keep on the road. So buying one of those would have cost 2.8k with 1.8k of that in tax so it's not exactly making car's illegal and keeping it on the road cost is only 200$ / month. You just need to find the loophole.
I've seen them biking when it's raining as well, but I think their roads and paths are prepared for it. As in, the surface isn't as polished as the streets here, so it's much harder to slip, unless you're as clumsy as... me :(
Oh and, you should have seen my dutchie friends biking on ice this winter, absolutely impressive.
Rain is not unknown in London. But even though you can do it cycling is unpleasant when it's raining particularly when, despite the carping, the alternative of public transport is as good as it is here. The Brompton lets me make the decision at the time rather than first thing in the morning.
Weather also counts. I don't think Amsterdam ever gets quite as warm as San Francisco, where I wouldn't want to be caught riding a bike on a warm day in a suit.
When I was in Seattle, though, plenty of people biked to work. Yeah, we didn't have bikes all over the streets, but it was a refreshingly good start.
I lived in a not very flat part of the Netherlands and most children went to school by bike (also if you had to travel >20km/day). Now I live further north (flat) and I can certainly say that I prefer biking uphill to biking against the wind (flat => more wind).
Bikes are often very practical in cities but not when it's raining and not when the gradients are significant. Despite the rain and minor inclines I have a Brompton http://www.brompton.co.uk/ here in London and adore it.