?? The frame is definitely not light, and it is definitely made from structural steel.
I've sawn close to half a million board feet on mine. It's 11 years old an has taken all the abuse I could throw at it. It cuts as true as the day I got it.
The pole mill down the road from me use a manual LT40 for years to salvage their oversized butt ends -- it had 6000 hours on it when they finally replaced it. It was still in good shape, but they couldn't keep up so they replaced it with an electric super hydraulic. That had over 8000 hours on it when they finally sold it. They'd have kept it but their market collapsed in 2008.
You'll find lots of people who have sawn over a million BF (and sometimes 2 or 3 million) on a Wood-Mizer mill.