You're right. No real answers, but apparently it is common knowledge within the Chrome community that these updates don't go out to 100% of users immediately.
The Google employee (Mike) on that thread confirmed that. I'm sorry there's not a way to manually force the update. I wish there was. One Chromebook user commented that he had just gotten v27 the day before (6/19 I think), so you're not alone. I'm sure there are others out there that still haven't gotten it.
If I had to give an educated guess on why it rolls out slowly, I would say they probably do it for debugging purposes. I'm sure it is tested quite thoroughly, but nothing is ever the same in the real world as it is in the lab, so they don't want to roll it out to 100%, just in case there may be some glitches that weren't found in testing. They wouldn't want 100% of users to get a "bad" update and then all 100% have to un-do the update or live with a "bad" update until the next one comes out (that would put a tremendous amount of pressure on the update team. I would imagine it's a lot easier to deal with a handful of "bad" updates rather than 100% of Chromebook users. It makes debugging a lot more manageable I would think. Again, I can't confirm any of that. It is just my educated guess. Hope that helps in understanding the situation a little. :)