That's pretty much for receiving multicast, it wouldn't matter though even if it's enabled both ways.
You have about a 99.99% chance the the first router you hit in the ISP cloud will filter multicast (at the very least, it's not multicast-routing enabled, or not enabled for User--> Internet).
Traffic utilization on the 'net would go through the roof, and of course there'd be folks that turn MC on and let it go forever...unnecessarily tying up the bandwidth.
If you're on an Educational campus, talk to the IS/IT folks about getting access to The MBONE, or Internet II....either will have some multicast traffic, and maybe allow you to send multicast.
Good Luck
Scott