Okay, so that part is not clear, but it is there...
How long has "GNU Free Documentation License, Version 1.2 or any later
version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts."
been at the bottom of the edit page? Just wondering.
Years. I don't know about since the beginning, but certainly a long time.
And in these cases, why hasn't wikipedia been completely compatible with CC-BY-SA since its beginning? I was under the impression the only sticking point were these parts.
I believe the GFDL requires derived works to be distributed under the GFDL, not just a license that is similar to the GFDL, so isn't compatible with any other license however similar it may be. (IANAL, YMMV, OMGWTFBBQ)
The statement at the bottom of the page should indicate the invariant exception btw, it is unclear that you are pointing to a document that needs further clarification, even with the link to Wikipedia:Copyrights, which btw implies that there might be cases where Invariant Sections could be included under the non-invariant GFDL version that wikipedia uses.
Linking to the verbatim text of an incomplete license isn't desirable ;)
It does indicate it - you just have to follow the footnote.