Is it really about the bottle being decanted, or being ensured you're getting the wine you asked for? If I order the vegetarian lasagna, but I get the beef lasagna I'll immediately realize something is wrong. I think that's less true for drinking wine, especially if you're not super good at sensing nuances.

Better restaurants serving older vintages will definitely decant, though I agree it's rarer than it should be.

I've seen a few use those aerating pourers, which is better than nothing.