Crab,
Civilian aircraft usually do not have the ability to monitor Guard (121.5/243.0) frequencies as do military aircraft. It is not a normal practice to do so anywhere in the world that I know of. It would be a good practice but probably impractical for Robinsons which usually will have just the one radio. There are other frequencies that require monitoring for normal operations.
If a TDA is put into effect and one is out of touch for good reason....how would you know of it....and thus be able to comply with the restrictions.
We have a similar problem here in the States regarding TFR's...which can be called for any number of reasons. If you are out in the 'bush", it gets awfully hard to keep track of these things even if you have all the best of intentions.
Or....am I off base here?