Please correct me if I am wrong, but once you start with root and leaked updates, does that not make taking advantage of official updates potentially more difficult if not impractical? For example, many people are wanting to root the Droid X to remove the preloaded apps and Blur interface but apparently removing some of the associated files can then prevent official updates from loading. At the same time, while root was achieved for the Droid X in Android 2.1 it seems to have been confirmed that the official update to Android 2.2 closes the exploit used for that root and root with Froyo has not yet been achieved. So rooting apparently can not play well with official updates.
The release of the Galaxy S phones across multiple carriers has also apparently lead to some interesting situations on yet another level with updates that Samsung supports but that have not been approved or authorized by the individual carriers. Supposedly Vodafone is one whose formal stance is that loading some updates that Samsung offers but that Vodafone has not approved is not only not supported but actually also voids their warranty. I can see a similar situation happening with Verizon supporting only Fascinate specific updates.
I have a different perspective for two reasons. First, I would feel better about overlooking some of the past support issues if there was an indication that things had indeed changed. However, taking what apparently will be three months or longer to address problems that seem to widely affect the Galaxy S phones released to date is not a good indication that things have changed. Since the thread is comparing the Fascinate to the Droid 2, a Droid 2 update that apparently addressed multiple initial issues was issued less than 2 weeks after release.
In addition, the Fascinate has not been released all over the world as while each of the US carrier phones may be in the Galaxy S family, each is also unique and differs in hardware and associated firmware. There definitely could be issues and updates specific to the individual versions that would affect only those particular phones. For example, the NAND memory that Eazail70x7 referenced would seem to potentially require some updates to be specific to the models using it. Similar for versions with a physical keyboard, front facing camera, carrier specific apps or firmware and so on. As noted above, addressing carrier and model specific updates and support seems to present some challenges.
Im not so sure they all differ in firmware maybe hardware yes but they all run the touchwiz and even with the nand memory i dont think that would slow down the update process but maybe i am wrong.
And about rooting , you will still get the updates you just may not necessarily get the os updates if you have already installed an OS for example 2.2, which is not always a bad thing because alot of the time the OS updates pushed by carriers have alot of bugs where as the leaked versions are usually a little cleaner