Ah, I think I see the problem. We call that "sarcasm". Quite a lot of us get that just fine, though of course the internet can always turn up at least one person who doesn't. "Irony" is reserved for events that are only ironic in the light of other events; death by drowning isn't "ironic" until it happens to a swimming instructor, for instance. You can't really say something ironic, it has to happen. (And if you say something ironic it is a description of a thing that happened.)
This is, in part, incorrect. "Irony" is in its original (from Ancient Greek) and primary usage a rhetorical form -- in other words, something intentionally used by a speaker. Experts disagree on whether "verbal irony" and "sarcasm" are the same thing -- sarcasm might require a kind of sharp, biting tone. But the original comment is certainly ironic.
A situation like your drowning example is also irony; sometimes to be explicitly this is called "situational irony" as opposed to "verbal irony."
Allow me to be pedantic right back. I did not say "sarcasm is". I said "we call that sarcasm". It's not really to label a description of how a word is used as "incorrect" and use a proscription as evidence. My fourth sentence was a bit regrettably absolutely phrased but the context of my statement should be set by then.
I don't even care if that's true of all of us Americans, it's true of enough. (The idea that Americans don't get "sarcasm" is very foreign to me; oh, I certainly know people who don't get it but we seem a fairly sarcastic culture to me.)
Okay. I think those sources are descriptive, but to be sure, here is the American Heritage Dictionary (http://dictionary.reference.com/browse/irony), an explicitly descriptive dictionary about American usage. It seems to agree with the other sources that irony can be and is often used in this case.
On the other hand, one can reasonably believe that every dictionary is, by its nature as a reference book, primarily prescriptive (and proscriptive) and therefore cannot be reliably descriptive. If so, then it seems we do have to go only with personal observations.
In terms of personal observations, I agree with you that many Americans I know would use "sarcasm" in this case and not use "irony." I think I (along with many other Americans, maybe fewer than the other group?) would use "irony" and probably not use "sarcasm" because it doesn't have that particular, hard-to-miss sarcastic tone of voice.