The expansions of Ω and Å are prohibited in NFC. NFC normalises them to U+03A9 and U+00C5. Perhaps HTML5 should make these entities align with NFC.
(i.e. same as Ω and Å)
HTML5 just uses whatever the MathML WG decides. I recommend taking it up with David Carlisle <firstname.lastname@example.org>, who maintains the source file.
Adding myself to the cc list for this bug.
(On the face of it the suggested change looks correct, but I need to think a bit about implications on systems that have made use of the existing (longstanding) mappings. So I'll delay deciding whether or not not to make a change.
I made this change in the editors draft for the xml entities spec
I believe the same unicode.xml source change will affect the