Sorry, I would like to disagree with Andromeda. The fact is that the companies make the contract and present this contract to buyers. Buyers are neither solicitors nor have easy access to right solicitor. Further the time period given for signature is usually 7 days. I can even say that the payments are always linked to the construction, sometimes they are linked to specific stages of construction such as Foundation and Structure etc. When they are not linked to a specific stage they are (or at least they should) be linked to general progress in construction. It is in my opinion very stupid to think that because the 'contract' schedule leaves 20% for completion. Why would a developer want buyer to pay 80% of the cost when there is no sign of structure.
I think if many buyers/investors approach Dubai authotities such as RERA or Dubailand with their concern, it is very likely that the Law will be amended to something like " If the start of project is delayed then the developer will ask buyers to pay more than 25% of the total cost".
Hope buyers of Dubai property will high light the names of such developers so that at least these developers lose some business in their future project, this seems to be the only way to tell the un-ethical developers to change their attitude towards their customers.