This is link-layer multicast. Because early Ethernet is actually a broadcast network, multicast worked fine there, and because so many subsequent network link layers are pretending to be Ethernet (including 802.11 "WiFi") they all have link-layer multicast too. Today that might mean smart "snooping" modes in switches, but in principle dumb equipment will work just fine, and in practice I've never had any problem with cheap home GigE or Fast Ethernet hardware too dumb to do snooping.
Any manufacturer that does even a little testing will notice if they've actually completely broken link-layer multicast on a LAN because such a variety of things break in that scenario, including features in famous brand name products like Office and Mac OS X.
But if their implementation does something dumb with multicast that only shows up under /load/ then these features (which are mostly discovery mechanisms, using multicast to avoid wasting CPU on uninterested nodes) won't trigger it. A multicast video payload, even on a LAN (so no actual multicast routing) will run into problems though, as will pseudo-reliable multicast file delivery and other techniques. Whoops.