I wonder why that is not a problem for example for EC2 US-West (the cheapest EC2 availability zone)?

us-west-1 is a great success. Just two weeks after its official launch its level of activity is 73% of eu-west-1, which has been around for a whole year!

http://www.jackofallclouds.com/2009/12/comparing-amazon-ec2-...

California is twice the area of Ireland AFAIK?