Huge?
That is (per 4e) - one size category larger than a Beholder, Dire Boar, Carriorn Crawler or a freakin' unicorn.
and the same size category as a Balor, Glabrazu, a common Dracolich (neither blackfire nor runescribed) or an elder (but not an ancient) black dragon or for that matter a fell troll.
To me, this smacks of Games Workshop changing the metaplot for WFRPG to bring it into line with how their tournament miniatures game turned out or L5R deciding the direction the game will go based on CCG tournaments. Neither of which I cared for. (of course, neither of those actually changed the stats of a critter in-game or other crunch....)
Yes you can, as a GM, handwave the size of the mini....but gee doesn't that kind of defeat the purpose of having the mini on the table in the first place?
(Though this does make me wonder - how many groups are actually ever going to meet Tiamat in an encounter?)