I know its not the number one cause, but you're forgetting the crap tarmac thats being put down now - since when have we needed new road signs saying 'slippery road surface' *after* its been resurfaced
The cheapskates just want a longer-wearing and quieter surface, and sod the grip levels.
Add that to the generally poor riding (and driving) ability of joe average these days and you get more bad accidents simply because they dont know how to read the road anyway.
[/rant]