I discovered, that Google changed some things in the actual Active Sync / Exchange protocol on Ice Cream Sandwich, because I wasn't able to use the Lotus Notes Traveler as Exchange account on 2.3.7.
So does anyone has a list which versions of Active Sync the Android versions use?
As with most Exchange ActiveSync clients Android implements a sub-set of features from various versions of ActiveSync.
According to the Android 4 (Ice Cream Sandwich) Platform Highlights, the Email client supports EAS v14 (scroll down to the "Improved email" section), in a comparison with Gingerbread (Android 2.3.x) though you also need to take into account the Android 3 (Honeycomb) changes which while they don't specify EAS changes did add support for policies for encrypted storage, password expiration, password history, and password complexity, all of which are EAS features.
There are probably more differences between versions than it's practical to keep up to date here, the Wikipedia page Comparison of Exchange ActiveSync clients has a pretty good table comparing feature support.