How do you ensure that they're answering it honestly, though? Or, less maliciously, that they're answering it with something in line with what you'd think is a decent work life balance?
Also, the people I'm asking are typically engineers, they're not inclined to lie about things like this, and they're not expert spin doctors. Plus, when I go for the full day interview and talk to many people, I'll ask many of them about it.
I worked for two young guys once who'd never had proper jobs, much less ever managed anyone before, and they had the cheek to have a go at me for only working my hours. I told them it wasn't my company and walked off. They couldn't sack me for working my contracted hours, regardless of if other people were working more for free...