And this is why you fail. Qualifications like an MCSE prove to a potential employer that you have been trained to a specific, well-defined and openly published level. If you tell someone that you have an MCSE with X, Y and Z modules, they can check the syllabus for those modules to see exactly what you claim to be able to do, and they can check your certification to make sure you actually passed what you say you passed.
If you just say you have 3 years experience with Exchange, for example, who's to say what that experience entailed? Creating and deleting a few email accounts? Setting the odd mail redirect? On the other hand, if you say you have 3 years experience AS WELL AS the MCP certification for Exchange, they know exactly what your expertise level is.
Plus, certifications show you have a level of professionalism. I mean this in terms of understanding the standard Microsoft/Cisco/ITIL/whatever path to problem solving, and also in showing sufficient commitment both to the industry and to your chosen career because you have a demonstrable willingness to invest time and money into improving yourself.
That is why certifications are important. If you want to reach the upper echelons (ie City jobs, positions high up in banks, £100k plus salary) this is the sort of professionalism you need to show.