I think if you send a Ruger SA 3 screw in to Ruger for whatever reason they will modify it and convert it to the "new model" with the transfer bar and it will no longer have the classic 3 or 4 click traditional single action.
I don't know this for sure but I am pretty sure this happens as it is a safety issue of big concern with Ruger, liability, as was mentioned.
It's not about a safety concern, it is a legal responsibility. Ruger LOST a lawsuit (that they shouldn't have lost, but the jury apparently went for the "deep pockets" of the gun maker, but that's another story), which resulted in the design of the "New Model" action, which hit the market about 1973 or so.
Part of the settlement agreement was that Ruger would convert all old models to the new standard. There was no recall, Ruger advised, but did not require owners of old models to send them in for conversion. However, Ruger is required (by law - the terms of the settlement) to convert every old model they get their hands on, no matter the reason the gun was sent in.
They HAVE to do it, or be in violation of the settlement agreement.
Ruger is indeed deeply concerned with their liability. If you aren't aware, a few years ago, Ruger stopped issuing a warranty on their guns. That's right, Rugers (today) don't have a warranty.
Ruger stands behind their products, and very well, but they no longer give a written warranty. Not because they are trying to weasel out of standing behind their guns, rather quite the opposite.
The various laws about what "must" be in a warranty are confusing, vary widely and may even in some cases be contradictory. Ruger simply decided not to play that game anymore. They stand behind their guns, but don't give a warranty that some lawyer can twist into a claim of them being in the wrong, when they aren't.
I respect that, a lot.