I must respectfully disagree.
I would draw a different analogy. The advent of spreadsheets in no way diminished the need for accountants. Certainly financial data is more available then ever before. Companies like Bloomberg have made a whole business out of trading on the professional analytics created and managed by accountants. There are dozens of different accounting packages like QuickBooks on the market today, and yet the accounting profession is alive and well. There are accountants that specialize in venture capital structures, others that specialize in capital planning for real estate investment trusts. If there is a significant business market in the world, there is a branch of accountants that has evolved an expertise to apply the principles of financial analysis and the Generally Accepted Accounting Principals to this area of business.
A similar pattern can be observed in the application of specialized geospatial education and training to a variety of problems from hydrology to transportation to the distribution of electric power. In many different areas, GIS professionals apply high-order geospatial concepts of spatial reference, topology, and geostatistical analysis to support businesses, governments, and non-profits. Proponents of the certification of geospatial professionals cite the requirement for education and training in these concepts along with practical experience in the use of geospatial technology as they make their case for establishing a true profession in this field.
Some of the comments on Don's blog suggested that because geospatial analysis is used in widely diverse fields that this somehow diminishes GIS as a particular area of study. I would argue that just the opposite is true. It is specifically because geospatial concepts, analysis, and technology can be effectively used to support a very wide variety of the world's problems that makes it such a compelling area of study in its own right. Certainly no one has suggested that the value of an MBA is somehow diminished because people who possess an MBA pursue a wide variety of interests.
From where I sit, the future for GIS professionals has never been brighter. As geospatial data becomes more available and the systems that can leverage that data become more pervasive, there will be a growing demand for trained professionals who understand the power of geospatial analysis and can bring that power to bear to help solve some of the world's most critical problems. If you truly want to make a difference in the world, and you would like to have a wide variety of choices of how and where to invest your energy then a Masters in GIS is a great place to start.