But still, I'm not quite convinced -- what features/benefits do they bring to the table, that simple IGMP multicasting doesn't provide?

Reinventing the wheel is almost always a bad thing, but would I really be able to reuse either of those wheels with less code than in Listing 1? And without any awkward runtime dependencies or license-baggage?

The point of this article is that everything you need to accomplish simple client/server rendezvous on the LAN is provided with .NET, out of the box.

Open Source? Heck, Listing1.cs is public domain!
-S