These arguments also hold true for international Internet exchange points. Several Web caches around an Internet exchange point will normally be set up as neighbors, unless one wants to route traffic through another network, which will normally not be the case. As long as a Web cache serves only local users at one location, network topology is not an issue. When you start to build meshes and hierarchies, topology comes into play. If you locate the servers of your meshes without consideration for the topology, you may end up generating more network traffic than without Web caching.
Some links are critical.
One prime example is inter-continental links, another is international links. Scaling is one more issue where topology knowledge is needed in order to build services and meshes of servers. An ISP is likely to know both what links will be upgraded and where bottlenecks are going to persist - and ISPs might be able to influence link upgrades.