W2W is an abbreviation for Wall to Wall. Wall to Wall posts have a different format than other FB feed posts. See image below for visual differences.
The top post is a normal feed post, having only one user name from who posted the story.
The bottom post is a W2W post, having both a story poster and a target user.
The HTML code and DOM structure in these posts is different and cause the script to do extra work to determine who the post is by. These posts are also meant for another person, however some games not only allow allow you to take them, but suggest that they are for everybody. Other games specifically bar you from taking them and warn you that the post is not meant for you on the acceptance page.
Because of all these odd possibilities for W2W posts, I've offered an option for each game to not steal W2W posts. It can be switched on or off if the Sidekick makes use of the option.
Due to current changes not fully distributed by FB, sidekicks may have some trouble using the "dontSteal" magic word. When FB gets the current change fully rolled out, I will begin patching this issue further. For now, all W2W posts will register as for you if the script cannot determine who the post targets quickly and easily.