Actually, the rear wheels usually take the corner a bit wider than the middle wheels. Depends on the exact bus model though, the currently most common version with engine in the rear vehicle swings out less afaik.
Funny though that they don't appear to cause any problems for cyclists here in The Netherlands, not even in some of our large university-cities with almost more cyclists than buses. Which actually even have 20 meter bendy buses (Groningen) or even 25 meter double articulated ones (Utrecht), also on quite narrow roads.
Road space taken by the bus seems not really to be an issue here, the main issue is the mass transit and thus how to get as many passengers in and out as fast as possible. Something that is more easily done in an articulated bus with four sets of doors than in a double decker.
Just to give an idea: when the double-articulated buses were still being used on route 12 in Utrecht they carried a whopping 4000 passengers an hour with a bus every 2 minutes. That was just a matter of arriving at the stop, squeeze ~133 passengers in the bus within a minute or so and leave again. Try that with a double decker