Read the following page:
http://www.mecoa.com/faq/breakin/breakin_abc.htm

The manual for the Tower .75 talks about possible damage if the wrong fuel mixture is used and the engine can't come up to the right temperature.

The manual that came with my Webra (ABC) under break in says the following: "Allow the motor to warm up to full operating temperature, otherwise it may suffer premature wear..."

I'm sure I could locate more, but hopefully you get the message that yes indeed manufacturers do say ABC engines should not be run sloppy rich, because it prevents them from reaching proper operating temperatures, and that it could lead to damage.