Of course everyone has the right to post about whatever they want, no matter how many times we've had the same question/variation of. And people should not be rude to those who ask questions.
However, if someone wants the best advice, it often would benefit them far more to spend an hour searching the archives. Those of us who have been here a long time are familiar with who the 'experts'/especially knowledgeable Mumsnetters are on certain subjects - be it MMR, nanny questions, good reading books for children, school admissions, housing authority, where to rent a flat in Paris, benefit information, remodeling a kitchen, Kumon, what to do in London with children, etc., etc, etc. Those posters have often posted thoughtfully, eloquently and helpfully in the past, and will not be inclined to post essentially the same information over and over.
For instance, sometimes I will see a thread by a newbie on a 'familiar topic' and think 'ooh, they need X on this thread because she can tell them exactly what they need to know' - but if X has posted several/many times before on the same sort of thread, she is less likely to repeat herself.
So, the most helpful, informative and authoritative information is often to be found in the archives. And the person asking would be best served by looking there. Obviously it might not give the same online 'interaction', but that is another angle....