I suspect so. The only reference I can find to "average"...

I suspect so. The only reference I can find to "average" survival benefit is from mainstream media, who let's face it, can't be expected to know simple mathematics.
I notice it's often misquoted as many people without statistical knowledge see little difference between median and average and may not see the harm in using them interchangeably.

More troubling is that I also can't find any mention of a 3.9 month benefit (median or otherwise) in any literature. The phase 3 trial results give Yervoy a 3.7 median survival benefit. So perhaps 3.9 could be the actual average, but I doubt it:

http://publications.nice.org.uk/ipilimumab-for-previously-treated-advanced-unresectable-or-metastatic-melanoma-ta268/the-manufacturers-submission