I've had the people who required "exactly 40 hour weeks", which typically meant a 45-50 hour week. I quit.
The managers I've had for the past 7 years or so have agreed with the fact that we are all adults. We know what a full work day is. We can tell when our creativity has run out for the day. Sometimes people will put in a 9 or 10 hour day, other times they may be done at 6 or 7 hours. All that matters is that it mostly balances out in the end and that they get their job done. We have had the rare individual who will abuse it, and routinely put in 6 hour days, but they are rare and are quickly dealt with.
Companies that regularly require a min of 40, and max of whatever they can get away with, is not where I work for long ; )
Where I'm at now, is more along the lines of your last paragraph... I typically work from home two days a week, and the other days, I'll be at the office between 4 and 10 hours, but my boss knows how much I contribute, and the hours I put in outside (including weekends)... It's not the same for my co-workers though, so it's not purely the business that is this way, which is unfortunate, but I'm fine with being a special snowflake ; ) So I typically put in 50-60 hour weeks, because of the flexibility they afford me.
Not surprisingly, I chose the flexible with me vs them ; )