The same requirement exists within the EU. As far as enforcement goes, generally speaking, it tends to be the airPORT rather than the airLINE. Once you've made it through the same big security checkpoint that everybody else with a ticket goes through, nobody looks at what you're bringing on with you (well, as long as it fits within baggage size limits, which might still vary by airline).
>From my experience since those rules were introduced:
US/British/Irish airports - strict enforcement Continental Western European airports - somewhat more relaxed enforcement Eastern European airports - ha