The concept of a "security theater" is one that is often used by security expert Bruce Schneier. It's used to describe "security countermeasures intended to provide the feeling of improved security while doing little or nothing to actually improve security." There's a list of examples, if you are curious... And I think that we might be able to add one to the list: London has bought some expensive fuel-cell powered electric buses and put them on popular tourist lines to showcase the technology. It's even likely that they bought the buses for the olympics in the first place. But these buses have now been ordered to stay parked during the olympics "in the interests of security", and the hydrogen refuelling station used by the buses has been ordered not to store hydrogen on location for the duration of the games.
Our colleagues at How Stuff Work have a piece about hydrogen fuel safety that gives more details on this, if you're curious.
This seems to be a case of people discounting the risks that they are familiar with (diesel) and fearing things that they aren't familiar with (hydrogen), even if it is likely to be safer.