On all the Regent "air included" itineraries we have looked at, if you don't take the air you get a $1,000pp price reduction. Don't know if this applies to the PG. But the catch here is "from Los Angeles." On all the other itineraries we have looked at, the "air included" applies to your city of departure.
This seems to bring the PG pricing closer to the pricing on the standard Regent ships with the exception of the Baltics and some Mediteranean itineraries. When you factor in the difference in the standards (smaller cabins, more crowding, and lesser food service) on the PG vs. the other Regent ships, it is probably equivalent.
But then we are booked on the Mariner in November, 2009 Sidney to Aukland and have yet to be quoted a price. We are keeping our fingers crossed! When we booked this 2009 trip we were not told there was a cancelation penalty.