An ATC (western Europe perspective) view.
It's true that modern transport aircraft have multiple redundancy but it's also a fact that aircraft do go comm fail. There are different reasons - there have been certain radios that go to sleep (I'm not sure whether the cause has been positively identified) and, hard to believe I know, but sometimes pilots switch the darn radios off in error (well, set the audio up in such a way that they don't tx or rx or both). But, admitedly, it is a rare event.
So there is a need for procedures to follow. A few years ago the radio comms fail procedures in Europe were revised and harmonised. The revised procedures reflect current reality in a high density traffic environment well served by radar. And that reality is that as soon as an aircraft squawks RT FAIL ATC will assume that the aircraft will continue according to the FPL and will try to move everything around it out of the way.
Now the likelihood of a comms failure happening - which is improbable - at the same time as finding the weather is below minimums - which is unlikely (given the proportion of flights that have to divert) - is very very small. Probably too small to write procedures that have any value (i.e. help the situation to be resolved in a specifically predictable manner). In practise, if an aircraft with a comms failure goes around the same thing is likely to happen as before the go around - ATC will watch what the aircraft does, move other traffic out of the way, and do anything and everything that it can to help. Add ACAS into the equation and it's hard to come up with a set of procedures that are sure to work better.
In different environments, however, the European solution will not be the best one.