Many lenders don't want to lend on the purchase of condos right now--especially new ones. One of the reasons for this is because they're so hard to value right now. Many lenders won't lend on condos in developments where the owner-occupancy ratio is less than 80%. Many lenders won't lend on condos where the HOA is in arrears. Many lenders won't lend on condos where the developments aren't FHA-approved.
If you're determined to buy a condo right now, then it's much better to buy one in an established community. Those are much easier to value, but your mileage will vary.
Anyway, the common charges on new developments are estimates, and those estimates vary wildly. Also, those charges are subject to various market forces. Keep in mind that the costs for building materials is in constant flux. The fluctuating gas/oil prices, the titrating flow of credit, and overall sluggishness of the real-estate market aren't helping the situation. However, that doesn't mean one can't create new models that will generate more reasonable estimates for now. You'll simply have to sample the data periodically, and adjust your projections according to the amount of risk that you're willing to accept.