Statcounter[1] puts IE8 at ~10%, 12% for the US[2]. In some markets it's even lower[3]. This matches what I see from non-tech client websites. For anything related to software, IE as a whole is close to zero.
StatCounter tracks 3 million websites vs 40k for NetMarketShare.
As best I can see on the site you linked, IE8 is 23.23%. That also disagrees significantly with this source: http://caniuse.com/usage_table.php where IE8 is 8.89%
Well one of the websites I'm working on is a fairly big one in germany and only about 4% of all visitors are using IE8 or below. Guess what! We now only support IE9+.
You combined all aforementioned versions of IE together to yield that result: http://www.netmarketshare.com/browser-market-share.aspx?qpri... — even combined the market share is still in my opinion minuscule. The only browser with a substantial market share is IE 8 which according to the site has a market share of 23%, it's not even worth adding in those other percentages on-top to try and make it seem as though a lot of people still use those browsers.
31% is not justification enough to maintain legacy code in a library that has become a little bloated over the years because of the backwards compatibility with older browsers. If you want to support that 31%, use the 1.9 branch it's better than the alternative being no support whatsoever.
Edit: Why all of the down-votes, is my response offensive?
Then shouldn't my original comment be the one that gets down-voted which is where I originally said IE's market share is minuscule, not my response to someone else's comment? I standby what I said. Considering Google does not support versions of IE below 9, Google too deems 1/3 of the Internet to be a minuscule proportion of users if they're fine dropping support.
Source: http://www.netmarketshare.com/