Here is the link to the Court's decision that led to the current practice on absentions. It's buried deep within the Court's archive subfoirum, and you have to re-set the search parameter to "from the beginning, but here's the link:
(click on this link)
Court decision by Chief Justice Byardkuria February 10 2006:
Erasmus:
Majority/50% rule
I interpretated, it seems completely wrongly, that the majority simply meant 50%. Just to make it clear... Majority means >50% of the cast votes. Does this count abstain or no? Since Heft and I said they wouldn't count.... can they lead to a runoff?
Abstentions, while not counted for victory totals, do constitute votes. As such, a majority is defined as more than half of all ballots cast, rather than half of all ballots cast for a candidate. So yes - if 90 votes are cast, and the totals are 44-43-3, a runoff would be required, as it would be difficult for either candidate to successfully demonstrate a mandate.
(bolded emphasis mine.) Although stated in the context of elections, this appears to be the origin of the current treatment of absentions in RA votes, although it wasn't part of the issue at the time of the linked Court decision.
Exactly how and when it started to be applied to the RA isn't clear to me, but this was the Court decision cited to me in the fall of 2006 for the change in RA procedure.