I believe it may depend. If the manufacturer changes his MSRP, its rare that anyone would charge more than MSRP. If, on the other hand, this is a "promotion/sale" by the manufacturer and the MSRP is still the same, then others would have the option to price at MSRP or below...
Of course there are always extenuating circumstances where warranties could be different or there is some sort of "tie-in" with another product etc. that makes apples to apples comparisons difficult.