They don't get that Touchwiz is much more than just a launcher. It customizes several aspects of the phone's UI. So, I took the time to compare Touchwiz and to the default Android UI. I took my Galaxy S and loaded it with a recent build of a Samsung's stock firmware (gingerbread.JVZ, Android 2.3.6) and compared the experience to AOSP (Android Open Source Project) by installing a nightly build of Cyanogen 7.2.
Admittedly this approach is not completely accurate as CyanogenMod comes with some minor modifications to AOSP as well. Also the galaxy S only supports TouchWiz 3.5, while the Galaxy S2 is shipped with TouchWiz 4.0 which contains some improvements to its predecessor.
I don't want to start ranting about TouchWiz right away, so I'll do the rant about it a little later.
The first difference is the Launcher.
Both offer several desktops that can be navigated by horizontal swipe gestures and a dock with configurable shortcuts. One of them takes the user to the "App Drawer".
The AOSP Launcher presents the apps in a vertically scrollable list with the apps ordered alphabetically. New apps are inserted at the appropriate spot so that the ordering remains alphabetical. Icons cannot be manually rearranged.
The launcher can easily be replaced by installing a third-party launcher (like ADW or Launcher Pro) from the Market.
The dialer is what appears when clicking the phone-symbol.
Another major difference is the calendar app. They all provide month-, week-, day- and task overview.
TouchWiz uses a dark theme for the calendar while the AOSP one uses a white background.
The Touchwiz calendar does not show descriptions for entries in the week overview. All day events are indicated by displaying a blue triangle at the day-label.
The TouchWiz calendar marks days as occupied as soon as there is one entry. The AOSP calendar displays the entries of the days as a bar.
The music apps look different but support similar features.
The main difference is that TouchWiz Music does not offer a widget, but a more powerful notification bar entry.
The clock apps differ quite a bit.
In addition to the alarm clock feature the TouchWiz provides a world clock, stop watch and a countdown timer. The AOSP clock provides an alarm feature and displays the weather on the main page.
The TouchWiz Messaging App follows the "iPhone-style" for displaying conversations.
The TouchWiz calculator offers a two-line display and a few more buttons.