It's often useful to be able to replace a power cord with a longer one -- depending on your setup the standard 2m cord might be too short. Extension cables are pretty unsightly, especially with big grounded plugs like the Schuko plug we have in Austria.

It's also useful in some setups to use power cords with right-angled connectors, because they make cable management easier.

Also, moving to another country is easier with standard sockets: just get a couple of new power cables from any random hardware store and you're good to go!