Yeah, they can't really have real-time shadows totally worked in, as it would make everything much more processor-intensive. Although I suppose it could be an option in the system menu...
Also, remember that Sam & Max is going to be for a more hardened adventure gamer market, and will look "grittier", so it would probably have better graphics (as "proper" gamers will have better PCs), and in a different art style.
Telltale has also said that CSI will also show that they can do different art styles. No one would want CSI done in a cartoony Bone style, so Telltale's engine is obviously very flexible.