FHA has guidelines regarding how many units must be sold and closed before and FHA loan can be used to buy a unit. So that is why the developer is making that a big deal. However, FHA changed guidelines so the property should be eligible for FHA financing prior to the 70% occupancy that they indicated. So if you want to use an FHA loan to buy in this project you should be working with a lender who udnerstands all of these rules and can make sure you are positioned to buy.
Also, other banks may be agreeable to providing financing in the project even if the developer says that only one bank can do it right now.
Hope this helps, but feel free to email or call me to discuss further.