AFAIK EHCache only does replicated (just like JBoss Cache).
Infinispan is designed primarily as a p2p app, and hence the lack of a server module or connector. However, we do realise that this style of architecture is useful to people and hence the REST server and ISPN-29.
In terms of network transports, Infinispan currently uses JGroups. RMI and JMS doesn't perform nearly as well for high volume systems, and the benefits (simplicity in implementation) don't really affect the end user (i.e., you). :)
If I introduce a RESTful server in the mix, will the cache remain distributed? I assume if all cache read/write go through the server, then eventually all cached data will have a copy in the server node. Am I right on that?