Just for the record (since most of the information in this thread is accurate), the games that have a seperate EGA release are SCI1. Later Sierra switched to what seemed a small step (both visually and version number wise) SCI 1.1, mostly called SCI11. However, internally, both systems are way different.
When SCI11 was being used, Sierra stopped releasing seperate EGA versions. SCI11 games were released with the "dither" driver EGA640.DRV. This technique was already used in older games, even Sierra's own Gamearts collaboration-games. However, this video-mode uses 64K video memory, instead of the 32K used in the "normal" EGA mode and most CGA/EGA systems probably didn't have that back then.
Anyway, some time ago I ran into the EGA versions when compiling this Sierra games version list... Anyone interested can find it here, among with some other Sierra stuff (debug modes, etc.) :
http://sierra.8bit.co.uk/
