Well, I'm a manager, so I would say yes, wouldn't I?
I genuinely think we are needed, in lots of different ways, but I know there are some crap ones out there. I see my main role as being the one who can step back a bit from the day to day doing, and look at the bigger picture. For the most part, I can trust staff to ensure that the necessary jobs get done toddy, but it's my job to look ahead and ensure that we all still have jobs to do a year or so from now. We need to move with the times, spot trends, anticipate threats, grasp opportunities etc. When you're busy doing the doing, it can be difficult to keep an eye on all that stuff as well. the manager is there to set the direction and to lead the way. They're also there to make decisions when people can't agree on the right way forward.
The same thing applies to staff development, as mentioned by a previous poster. It's my job to identify development opportunities for people that they might not see for themselves - for their own career development and for the overall skill set of the team.
It's my job to ensure that all staff provide a consistent level of service to our clients, so that the client knows that he/she can expect the same standards regardless of who they deal with. In the same way, I have to ensure that staff follow consistent systems and procedures - left to their own devices, we'd probably have a dozen different systems on the go, and that leads to mistakes, confusion among staff and a poor service for customers. I know this to be the case, as it's exactly what I inherited when I first took on my current job.
Then there are the people who take the piss, or those who just can't do what is required of them. I've had to deal with a few of each, and it can be hugely time consuming. However, if stuff like this wasn't dealt with, it would be hugely unfair on the hardworking staff who would end up picking up the slack. Dealing with underperformance is probably the shittiest bit about being a manager, but someone has to do it.
Likewise, someone has to be around to take responsibility for the stuff that might go wrong. The budget won't manage itself, for example, and if nobody had ultimate responsibility, it could easily spiral out of control. The buck has to stop somewhere, and usually that's the manager.
I think a lot of the problem is that people often don't see what their managers do, and so they assume they do nothing. I've been guilty of thinking this myself at times in the past, but I know that I add real value in my workplace, and I can see the value that others are adding too. For the most part, I think my staff would agree with this - but I'm sure the woman I sacked for incompetence wouldn't, and neither would the member of staff that I'm currently taking through disciplinary. So I guess it all depends on perspective. 