The primary reasons people use dedicate mrouters is for reliablity and
the fact that that's they way they used to have to do it. (Cisco's didn't
always have multicast routers). Its run on lots of real world networks
tho, Cisco, Sun, old NSFNet, several of the large nationals will
feed you multicast.

The main issues with multicast according to nanog, are configuration
and policy issues. Current mrouting protocols don't allow for policy
based filtering, but there are people working on it.