I'm guessing Russell Baker has retired (too bad, as he is great in my opinion.) But I wonder why he hasn't been replaced? It seems like lately no one introduces Masterpiece Theatre, which was, I thought, supposed to be an important part of the show.
My guess is that there is just not time for it anymore. Many series are now made with the American or aftermarket release in mind. They have to be kept at about 54 minutes or so I believe. A good example of this is the This Old House Series on PBS. Years ago they were about 28 minutes + long, now they are a bout 23 minutes long. This is so they can be sold to the DIY, A&E, etc. ntworks, and still be able to fit in commercials.
In my opinion, Russel Baker could not hold a candle to Alistair Cooke though. In fact Masterpiece Theatre, now just called Masterpiece has been on a decline since the mid nineties, if not earlier.