Ah, I didn't mean ALL of them, just the few you knew off the bat weren't right.
I see what they did the Borghese is list the actual ticket price without the reservation fee you'd pay if purchasing in advance. That's an odd duck 'cause, as you are required to make reservations for that one even with the pass, the extra € 2.00 fee applies.
Full price ticket: € 13.00 + € 2.00 reservation fee = € 15.00
Reduced ticket without pass: € 6.50 + € 2.00 reservation fee = € 8.50
Reduced ticket with pass - € 6.50 + € 2.00 reservation fee. =€ 8.50
Some others others that I looked at, such as Terme di Caracalla and Museo di Roma in Trastevere are correct...
€ 4,00 reduced fee the door for Caracalla, no advance reservation necessary, and €5,00 at Museo di Roma in Trastevere
...and some are not.
Castel Sant'Angelo looks to be off by € 2.00, and combo ticket for Museo Nazionale Romano is off by € 1.00 or a few euros more if there's a special exhibit.
The Roma Pass FAQ does state that "Please note: fees refer to the ordinary price of the museums; during cultural events and exhibitions, the price of tickets may vary. Some temporary exhibitions may have an added cost to the ticket, even for visitors entitled to gratuity." This may or may not be affecting the listed price at Musee Capitolini.
Anyway, Mei, you get the idea? Some of the R.P. listings may not be completely accurate but they're not off by very large amounts, and I'm pretty sure they can't account for ALL temporary exhibitions here and there. Just use the listing as a rough guide. :O)