Blu and HD DVD are basically the same. they are closer than anything else we have talked about. I only have single disc HD DVD and they are as thin as blu, just maroon
As for single disc blu, I have a few hundred of them and they are much thinner. Multidisc blu USED to be thick, as shown in the blade runner pics, but now it seems they are getting scarce. Case in point, many multidisc blu rays now have the second disc slot be on the inside cover as opposed to an additional piece of plastic, so the thick cases are no longer as needed. I see them more for TV series, Disney films and anything else 4 discs and up.