You raise some interesting pts AV; and probably have a far better take on how the books and lines work than me.
Have spent some time at the TAB with their books though for a feature I did for the paper - covert operation for personal reasons too
I don't really get it either - as you say, the ML should give a fairly standard spread in relation - although often they get a bit tight on the dogs; eg the Blues are $2.60 v the Canes and the Chiefs $3.50 v the Brumbies but the difference in spread probably won't be much more than a point. Do they wait until other books release their spread? Probably.
Your 2nd pt may be close to an answer. Sports betting is still at a very raw stage in NZ and I wouldn't be at all surprised to find that they still get a much larger % of sizable wagers on the ML rather than the spread; ie a lot of Kiwi punters who fancy themselves as big spenders probably don't know a lot about value and play the heavy chalks.
The TAB doesn't often move a line - I think the Reds/Highlanders line moved a couple of pts last weekend (in favour of the Reds), which was a real rarity. Their usual ploy is to move the odds; eg from $1.85 down to as low as $1.65 in some case, although usually just to $1.80. Which makes me again think they aren't getting a lot of big spread/points start plays.
That's why I always check their lines (points start-wise) for all NZ sports. I know they have had to set their own lines and I now their info may not be as good as mine
