The AC adapters for a lot of equipment seem to be specifically designed to block the AC outlets around it (this is in the US).
Is this a safety feature to minimize the power to that outlet or just lack of common courtesy?
It's not as if engineers sat around and designed them to block adjacent plug points. They are large because of the physical size of the components that they need.
With newer technology, and lower power devices, some AC adapters no longer do that, but for larger devices that is likely to be an issue for years to come.
One solution is to use a cable extension between the AC outlet and the adaptor.
The kind of adapter you are referring to is called a wall wart. To quote the article referenced :
The wall wart hence h*as to accommodate for all the components needed to the switching and matching and also accommodate for the transformers size which is required to handle and do the switching. The larger the size of the transformer,the larger and heavier the adapter* thus blocking up the surrounding area making it difficult to put in other outlets.
Here are two examples of inbuilt transformers for linear and switching power supplies.
That said its pretty bad design and there are a lot of complaints about how the system was initially designed.
IMO they are not designed, just engineered. With due respect for engineering, which is a must. Design seems to be considered optional.
Since some time ago I see bricks without a transformer, the component that made the old ones heavy and bulky. Modern power supplies are smaller, lighter and colder.