It does later.
Originally there was no differentiation between root and snare attribute modifier. They were both movement. Some roots still have the movement -10000% attribute if you look through the spells. It wasn't until velious that they introduced the new effect attribute of root that it was possible. Right now, sow snare and root are essentially identical for stacking purposes.
As far as pet taunt is concerned, pet aggro, bard swarm kiting, and tank threat are all pretty much operating with bandaids on them if at all. One of the original projects I had slated was a threat calculation overhaul, but doing that correctly would take at least a full month, and it's been 'good enough' that getting the content out has taken priority.
Dot stacking is working correctly. There might be an odd stacking issue here or there, but that's another velious change. You could find the answers to all of these questions in patch notes.
http://www.tski.co.jp/baldio/patch/19992002.php