Is the subscription of merge replication only for SQL Server Compact Edition?
This only means that if you are using SQL Server Compact edition, that this edition can only be a subscriber, not a publisher. 

Here is more information on setting up merge replication between Microsoft SQL Server and SQL Server Compact 3.5.

Here is an example of a different subscriber than SQL Server Compact edition, a blogpost which sets up a Merge replication using SQL Server 2012 as the publisher and SQL Server 2008 R2 as the subscriber:

Merge Replication Step By Step