There is definitely some variation in the brightness on the Kindle Paperwhite. There have been a few people who have exchanged them and they get the new one delivered before they have to send the old one back so have two units in front of them to compare. I've no idea if the same is true of the Glo though?
key thing is that everyone's eyesight is different, so it's hard to please everyone. On the whole though it does sound as if the light on the Glo is a little too bright, hopefully it will be something they can alter with an update to the firmware.... even if it is though who knows how long before they actually get round to a fix for it.