MFC is forcibly enabling cleartype when segoe UI font is found. This happens in afxglobals.cpp, where the following code is run
lf.lfQuality = 5 /*CLEARTYPE_QUALITY*/;
This is happening in the vs2010 MFC as well.
I would imagine this is being done because MFC must use the segoe UI font instead of the system default font. I'm not clear on why MFC needs to be doing this. It is contributing to a ghetto chaos rotted appearance which makes windows software nowadays frequently resemble a 1997 linux desktop. It makes MFC parts look wrong compared to other parts of apps which take pains to be respectful of the user's configuration.
Understandably, the segoe UI font was not designed to be used without cleartype. And that is why someone thought it was wise to add this code to force cleartype. But, anyone who has disabled cleartype would rather see ugly apps than cleartyped apps. I feel confident speaking for them.
Finally, I know MFC can be caused to use the system default font. I am not looking forward to asking every developer of MFC software to change his code in order to bypass MFC's font trickery. I would rather system libraries use the system default fonts as a default font.