git-subtree is not the same as a subtree merge. The author himself likes to point that out. A subtree merge is a one-time operation. git-subtree, on the other hand, enables you to continue to merge in upstream changes. You can also split the subtree (including it's history) from your repo and make it a standalone repository again.
Thank you for the clarification. Quoting the author:
“[Subtrees] are also not to be confused with using the subtree merge strategy. The main difference is that, besides merging the other project as a subdirectory, you can also extract the entire history of a subdirectory from your project and make it into a standalone project. Unlike the subtree merge strategy you can alternate back and forth between these two operations. If the standalone library gets updated, you can automatically merge the changes into your project; if you update the library inside your project, you can ‘split’ the changes back out again and merge them back into the library project.”
I guess I will have to get used to the idea that linking external repositories is harder than Subversion externals :) Which have serious limitations, I know, but at least they are so simple.
