The argument can be made that the market value assessed by bank sponsored appraisers and those commissioned by private parties result in very different values - one thought to be too low, the other higher and 'more accurate.'
Only homes that are currently under contract with the buyer using financing are affected by the bank sponsored appraisal values. Other homes will sale for cash, or financed buyers who choose to pay the difference between the bank's appraised amount and what they know to be the accurate market value. If demand is present, market values will reflect that demand.
Appraisers will always be dependent upon recent comps/sales to appriase value and thus, will tend to lag behind a fast paced, heating market, but they will catch up, because supply and demand are the true market drivers of real estate values.