You're right. Muller's comment there is head and shoulders above later remarks by GS (and much of the arguments made on their behalf).
As to your question, yes, you do have to say "sorry" or "I apologize". You also have to avoid criticizing those you've wronged while doing so and in subsequent statements on the matter.
Specifically, you have to avoid saying things like this:
"I have to be honest: All of these charges of extortion are distressing for someone who has worked so hard to try and encourage open and honest communication between companies and customers. I know that the pile-on effect is in effect here, but to hear it told in these comments, we’re evil people who are trying to exploit people in the worst way. We’ve always been simply trying to help improve the way companies do their customer service and make it more human. We apparently need to be better at explaining the way it works, I suppose.
"And now, I’ll step aside and dodge the bottle I see sailing through the air in my direction."
It's the attempts to evoke pity for them and cast any criticism as mindless persecution by people who aren't smart enough to get them that create more hostility. When you're in the wrong, it's just not time to go on about how you feel hurt by people being critical of you.
More appropriate would be, "We work very hard at trying to encourage open and honest communication between companies and customers. For that reason, I find it very distressing that our efforts could strike people as evil or extortionate. That is not in any way our intent, and we are looking at ways to better explain how what we do works."
Do you have to use the word "sorry" to express regret/"mea culpa"? All of that stuff felt pretty apologetic to me (comments, blog posts, etc).