It sounds difficult to broadly describe all uses of "I'm sorry" since the phrase can take on so many forms, like LL wrote. But I tend to think of "I'm sorry" as a necessary but imperfect way to function with the rest of society. Of course there's nothing to actually apologize for sometimes, but it's a way to sound polite.

"I'm sorry" is nowhere as irritating as when people assume emotions and feelings for you. Especially when it comes to how much your life should suck according to them just because of sight loss.

I'm blind and do have a reduced quality of life. My life was almost perfect back when I could see, even when my sight was as low as 5% (20/400 or 6/120( with a very low contrast perception; but ever since going blind I can only think of killing myself, so the I'm sorry is not lost on me. I'm actually glad that people understand that it sucks to be blind.