So why is there a new restirction on the size of hand luggage? The smaller size that they are allowing is, oddly enough, the same size as a laptop bag. This should keep the all important business travellers happy. But you are not allowed to take on hand luggage that was previously allowed. Obviously the size of bomb you can fit in a laptop bag is not large enough to cause serious damage, whereas larger hand luggage is more unsafe.
The airlines are taking this opportunity to reduce the size of hand luggage, something that they have been trying to do for years but have found difficult to do so far. Now they have an excuse.