Samsung has now justified why it cannot give the Ice Cream Sandwich update on both the devices.

Samsung has now justified why it cannot give the Ice Cream Sandwich update on both the devices. Galaxy S maybe similar to the Nexus S but Samsung says the smartphone and the Galaxy Tab run Samsung specific elements like TouchWiz UI, video calls, Samsung widgets, carrier and country customizations that makes difficult to run the new OS smoothly. The RAM and ROM storage are also an issue, Samsung said.

http://sammyhub.com/2011/12/23/samsung-justifies-why-galaxy-s-and-original-galaxy-tab-cant-be-upgraded-to-android-4-0/