As I recall, there is a quote from Tennant (at the stage door in Stratford) saying he didn't see the point to a DVD as that would invalidate the "theater experience."

I can see that being a very valid argument while the play was still running, which is when people originally started clamoring for a DVD to be rushed to market. And it is certainly not the same as seeing it live, but as a fundraising tool for the RSC alone it would be worth its weight in gold.