The cut-rate airlines, sure. The point of these recent warnings is that the majors are also seeing this as a potential revenue stream. Plus, many people (including us) pack the carry-on, and then hope that they will ask for "gate checks" at the gate. We volunteer quickly, so we get a free checked bag instead of having to pay $35 for it (domestic). We keep all our in-flight essentials in our "personal items", which are easier to fit in the overheads**. Less of an issue with the international flights, which typically use the larger Boeings or AirBuses.

And some of the rules are TSA, independent of airline. Like size of lithium battery cells ("power banks").

**Our last flight was on a Embraer 175 (I think), in which our legal carry-ons wouldn't have fit in the overheads at all. I saw several people not able to fit their bags in the bins because they were smaller even than the 737 bins.