I agree with Xavier a target-group is something at a higher level than a target.
I think that the key feature of target-group is dependency injection but as Xavier says "if thread-group is the only way to have target dependency injection, then people may use it only for that, and complain about the distinction in project help". The fact is target-group is not only a way to have dependency management, but a "new way" to think your build-script. I guess for us target-group is useful to make build modules easily reusable in a standard build (with standard target-group), without requiring any specific orchestration. This means target-group allow you to have a kind of "generic target", that's why in EasyAnt we want to have separated help for generic targets (target-group) and specific target (normal target). In addition, as we use target-group to have more "genericity" we doesn't want to have prefix on those "generic" targets.
