Are you really this naive? A lot of companies layoff/push out the bottom 10% yearly, this includes Microsoft. Not always done by fiat but via performance improvement plans aka PIPs.
Please point me to this Utopian company of yours that guarantees a job for life with no performance evaluations, layoffs, reorgs, etc.
"If you work for a company that isn't laying off people then turn over is 100% voluntary attrition"
No, that's called attrition. attrition by definition is voluntary, dim-wit. Turnover is the combo of both. Most Companies affect a "layoff" by PIPs.