I think the board users were well represented in the vote,
because it was widely advertised through direct notifications on hobby board threads.
The board was (ant still is) getting too much vandalisms to hold a vote peacefully.
That is why they resorted to vote at the external website.
Below are a few examples of the notifications sent to individual threads.
http://yomogi.2ch.net/test/read.cgi/hobby/1406426904/245
http://yomogi.2ch.net/test/read.cgi/hobby/1417449924/28
http://yomogi.2ch.net/test/read.cgi/hobby/1412700326/239
http://yomogi.2ch.net/test/read.cgi/hobby/1415536104/11
The sentaku.org website is sort of recognized among Japanese internet users,
as shown by this 2ch thread that's been maintained for years:
http://toro.2ch.net/test/read.cgi/esite/1399363493/ 【みんなの投票所センタク１１【対応だ！】
http://toro.2ch.net/test/read.cgi/esite/1377074093/ 【みんなの投票所】センタク10【IP解除して！！】
http://toro.2ch.net/test/read.cgi/esite/1365766772/ 【みんなの投票所】センタク 09【一部ウザい】
http://toro.2ch.net/test/read.cgi/esite/1356181185/ 【みんなの投票所】センタク 08【だが最近は…】
http://toro.2ch.net/test/read.cgi/esite/1344602144/ 【みんなの投票所】センタク 07