I have to laugh with all the nonsense replies about spy theories, gestapo practices, etc. which are uttered in this thread. High trees catch a lot of wind, I guess, so it's so easy to understand the bashing of the world greatest saw producer, being Stihl.
Every company selling its products in the US is vulnerable for being confronted with possible lawsuits that can ruin your company. Blood pointed out the single reason why Stihl sends out that particular message : it's to protect their ass, and from a legal point of view, it's absolutely smart instead of lame to sent out those messages to endusers and partners in the field.
It's a clear sign that the manufacterer cares about the safety of their customers, hint hint.
But that said, Stihl doesn't give a hoot if you modify your saws after they have done their duty to inform you of the risks. It even is good for their spares business and warranty claims budget
To those that perform paid mod jobs for third parties, my single advice is to have a good liability insurance.
To those that have a tree business employing staff, my advice is to not let your staff run anything but stock saws.
America is a nice country but their lawsuits are no joke.
Stihl knows it all to well.