http://bugs.winehq.org/show_bug.cgi?id=22765
--- Comment #17 from Igor Tarasov tarasov.igor@gmail.com 2010-05-24 05:30:34 --- Because there is non-subpixel (grayscale) font anti-aliasing. Sub-pixel anti-aliasing (implemented as Cleartype in Windows) is intended for usage on LCD monitors. http://en.wikipedia.org/wiki/ClearType
So, setting "none" to "rgba" field does not mean "disable all anti-aliasing", but rather "do not use sub-pixel anti-aliasing, instead use grayscale anti-aliasing".
Any anti-aliasing could be enabled/disabled through "antialias" field in .fonts.conf.