I think that’s probably about right. And even for founders, it might be getting an “urgent message” at 9pm from an employee or customer that is actually not-so-urgent.
In either case, what’s going on is nothing more than a process breakdown. Managers should create space for personal life — because the alternative is mutiny and disengagement. Likewise, the startups and businesses themselves should become mature enough that rapid response from a founder/employee off-hours is never really necessary, except perhaps in rare/extraordinary cases. In the regular case, someone “holds the pager” — or, it can wait until tomorrow.
As for your broader point about “work-life integration”, I think you’ll find many founders of companies nodding their heads, while some employees might be shaking their heads.
As a startup founder, you have made a decision to make your life about creating this thing (a startup) that other people refer to as “work”. It’s only natural that for you, the idea of work/life separation is somewhat nonsensical — similarly, perhaps, to how most artists find art/life separation equally nonsensical.
But some people choose to join companies and not have their work life become their personal life, and that’s OK. I often say at Parse.ly that I want to hire “work connoisseurs, not workaholics”. That is, not people who work all the time, but people who appreciate what work means, and choose their work — what they decide to invest their professional time in — very thoughtfully. Since work is most of your waking life, I’d prefer not to be working with paycheck zombies!