Maybe I'm in a middle generation? I'm certainly comfortable with programs where you have to save to a file, but for as long as I can remember, always every program I've used that doesn't autosave warns if you try to close it without saving. Web apps mostly autosave these days, but those that don't will also usually trigger the browser's "you may lose changes, do you really want to navigate away?" warning.

In my (I guess biased) opinion, this is a reasonable affordance to expect; throwing up a confirmation dialog is a lot less burdensome than implementing autosave. I would consider not doing so in this day and age an antipattern.