Samsung has officially said that the highly popular Galaxy S phone from 2010 and their original Galaxy Tab will not receive an update to Android 4.0 ICS. Apparently, the reason for this is because there is not enough room on them.
That's strange because, while I may believe Google that there wasn't any room left for the Nexus One to update it to ICS, since it only had 512 MB of internal storage, including the free 150 MB or so, saying that the Galaxy S didn't have enough room, when most of the units had at least 8 GB of internal storage doesn't make any sense. Even if they somehow limited the storage for the OS in software, I'm pretty sure they could remove the restriction, and make the internal space for the use a little smaller, so they can put the ICS OS on the phone.
Another reason they say is because of Touchwiz. Well, I'm sure a lot of users would appreciate getting the stock version of Android 4.0, too, even if they don't get to keep Touchwiz. But I'm thinking they really don't want to get rid of Touchwiz, and even for the Galaxy S2 version of Touchwiz, which they did update to Android 4.0, they kept the UI almost the same as before, and updated only the under-the-hood code. Again, this is something some GS2 users will probably be disappointed with. It might not be until Touchwiz 5.0, when they finally adapt some ICS UI style, if they ever plan on doing that.
Another issue could be the performance according to them. We've already seen some custom Android 4.0 ROM's on single core phones, so I'm not taking this answer for granted either. The web so far has taken up in arms against Samsung over this, and I think they will eventually agree to update the Galaxy S, and maybe even the Galaxy Tab (although less likely) to Android 4.0.