Fallout3 is much higher than 10% as well. The hard copies are 12% alone, then factor in Digital which probably multiplies that by 2.5, possibly 3x if you factor in Steam Sales.
I recall reading somewere that Fallout NV sold less than(or was it around?) 20% of total sales. Pete also agreed with Todd about the numbers.
@Enossirq, Look at current multi platform games for the best indicators, using OB is silly regardless of whather its part of the series or not. Back then there was no PS3 release. So of course OB would have a higher %. And the 360 install base was much less than what it is now, there is no point bringing up OB too much has changed.
FNV wound be the closest we are going to get to the open world rpg crowd that likes Beth games(like me), then you can look at other multiplatform rpgs,etc