[Why is there so much high-poly mesh in SL?]

There are tutorials on low polygon modelling online.  They're not specifically geared towards SL, but polygons are still polygons, so the principles will still apply.  

[Rigged mesh using Lightwave?]

I've been using Lightwave for making mesh with good results, and the COLLADA exporter in Lightwave 2015 seems to do the job with unrigged mesh.  The problem is when I attempt to import or export rigging.  When I attenpt to import the standard SL av the rigging either vanishes, or gets distorted.    Has anyone else had any success rigging mesh for SL, or is this a case where you can't get there from here?

[Why is there so much high-poly mesh in SL?]

Sloppiness, really.  Designers who are just not paying attention to the render cost of all that nice detail, and in a lot of cases not really thinking about whether they actually need all those polys to get the effect they want.