I mean honestly, when you stop to think about it it is clear they're not completely on schedule since they do want to make sure ARR's release go over hell of a lot better than 1.0's release so they're definitely taking their time to make sure everything is right even for alpha testing which these days are usually at least polished to the point it's only missing a majority of it's launch content.

For example in ARR Alpha it could have every Gridania quest for testing since it will let you not only test basic mechanics but test the actual flow and see how it is but it will obviously have no dungeons or crystal tower, this is likely the point they want it to be and clearly end of September isn't going to be enough time for it.