agreed with GmatGuruNY -- yes, there are PS problems that give unnecessary information, but they are rare.

presumably, these problems are rare because this whole idea (deciding which information is / isn't necessary in order to solve the problem) is the central theme of DS, which already encompasses half of the math section.
this is also the reason why you hardly ever see PS problems on which the last answer choice is "not enough information given" (such as OG12 #180) -- because that's already the whole purpose of the DS section.

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incidentally, the upcoming changes to the GMAT (scheduled to be implemented in 2013) tentatively include lots of problems on which most of the information is irrelevant.
one of the major new problem types presents an entire page full of quantitative information and then asks a series of questions, each of which requires you to use only one or two pieces of information from that entire page. it's up to you to figure out which pieces of information are relevant to each question.

the reason for the increased emphasis on this type of problem is that, honestly, it's an essential skill for anyone who wants to work in management.
think about the situations that managers encounter: there are hardly any situations in which the manager is simply handed a complete set of information -- in which all facts are relevant and must be used -- and asked to make a routine decision. instead, almost all important decisions that a manager makes, in general, involve sorting through a great deal of information and deciding what is, and what isn't, important.