I think the question is flawed. 1) We don't cater to IE9, which is at 5.11% according to stat counter. IE9 is a bad choice point for this - it's the first IE that had auto-update. Everyone left. We're catering to IE8+; 8 is currently at 6.5%. 2) You don't count the version; you count the version and all its successors. That is, we're not catering to 8, we're catering to 8+. 8+ is at almost 35% and is still the domina…
Why bother? in a few months it will be 5.5%. Next year it will be 1%. Why invest any time or attention to a browser whose market share is low and continue downwards into nothingness?
Do nothing. The IE8 problem will work itself out naturally. https://www.youtube.com/watch?v=Lz9810Y7ZRw
"2) You don't count the version; you count the version and all its successors. That is, we're not catering to 8, we're catering to 8+. 8+ is at almost 35% and is still the dominant aggregate browser."
That's just a sleight-of-hand obfuscation. If 9+ is 30%, why quibble over the extra 5% (and only dropping over time) that IE8 will offer. It's a diminishing return adding an older browser to the browser support list.
"5) The web solution for this is WAI-Aria, which began in mid-2012, and became a candidate recommendation three months ago."
No, WAI-ARIA became a Recommendation in March, not a Candidate Recommendation. The distinction between the two is two independent implementations.
"8) As far as I know, no single group of disabled users reaches 1% of the user base."
* Colourblindness (8% of Caucasian Men) * Dyslexia
"9) ... Your site has no aria markup at all"
The non-presence of ARIA does not make a site inaccessible.
"12) In short, because like you, most small web authors are more comfortable writing about the problem than being part of the solution."
Unfortunately, you are presenting the opposite side of the problem. So you have a little more knowledge about accessibility issues than the OP - but not enough to pass a quick scrutiny.
Perhaps, what is needed is for you and I to stop being part of the problem of disseminating half-truths, and spend that time quietly doing our jobs properly, and showing the results of these. Invest the time to teach someone else how to build accessible websites, and encourage them to also share what they know.
In all fairness, the poster of the blogpost has a fighting chance of improving her skills. She is worth teaching, for the scales of dogma have fallen from her eyes, and she is enlightened.