It seems that Samsung has made up their mind and even though they haven't even finished rolling out Android 2.2 for all their Galaxy S models, they're committing to upgrading them to the latest Android version - Gingerbread, or Android 2.3.
Samsung can't get away with just one update for their phone this time, although I doubt Galaxy S will get Honeycomb or whatever the next version for phones is after Gingerbread. Customers have come to expect constant updates from manufacturers, especially when Google is releasing new versions every 6 months. Samsung has 2 choices: either it keeps up with updating their phones, or they start making more stock Android phones.
I believe they will start experimenting with more stock Android phones, too, especially if Nexus S will sell well, and if carriers don't put too much pressure on them to install their own apps on the phones (or worse - Bing!).