I'm not surprised since it looks like the current story is setting up 4.0. Now had the expansion its own isolated story then I can see it only needing 2.x finished. However if it didn't need you to finish any main story or just 2.0, then at what ilevel would the gear start and end at? 3.0 picked it up right after 2.x with a i115 overlap. If 4.0 didn't need 3.0 main story then would the starting equipment and content be back to lv 50 with i150 and be the same level progression as 3.0? Otherwise imagine it not needing 3.0 or 2.0 main story finished but a average of i275 gear on a lv 60 job to access it. If anything that is another way of saying do main story to unlock content that'll get you gear needed to access the content.