j_b -
You make a good point. In the realm of wine in general, I agree with your assertation that a 95 point wine should have an exceptional finish -one that lingers and keeps you thinking about it for while.
For me, and my arbitrary wine rating scale, I use the typical points of reference when gauging a wines "worth" Nose, palate, mouth feel, body, finish, etc.. However, I don't necessarily assign more weight to any one category. For example, I was at a Clarendon Hills tasting yesterday at the local shop. They were pouring a complete range of Grenache and Syrah (for some reason they don't call it Shiraz?). Anyway, one of the Grenache bottlings had slightly aobve average characteristics but the finsih was amazing. Decanter and I were there and we both stood in silence enjoying the finish for several seconds. Had it not been that finsih, I wouldn't have paid much attention to the bottling but, the fact that the finish was so remarkable gave the wine a bit more "worth", to me.
So, with the '77 Barros, the combination of all the other characteristics are so appealing to me, I'm willing to give a little on the finish. This wine makes me really happy when I drink it and I haven't had that sensation with a "dessert" wine since d'Yquem.
Perhaps others will disagree and say that a wine needs to exibit every characteristic profoundly in order to merit that high of a score, but I feel comfortable making an exception in this case.
Of course, by the time I tasted these three, I was not exactly in "tasting prime" if you know what I mean, so the fact that I mentioned the finish at all could mean something.

Thanks for raising this question, j_b.