Modelling Escalation in Development

Escalation is a critical lever in preparing real estate development project feasibilities. In Australia, 4% and 3% are very common to be taken as the revenue and cost escalation, respectively.
However, there are some developers that assume price and cost escalations are the same and equal to 3%.
This raises two important questions; should cost and revenue escalations be the same? If not, then what should be the difference between the two?