Writing a biography is a serous thing, and Wikipedia entries, though helpful, are not the same thing as a dedicated, well researched and well prepared biography that takes several different aspects of a person's life into account. That's not to say that Wikipedia details aren't accurate, they simply are not an entire picture of a person with the kind of integrity of a serious biography.
Wikipedia is an encyclopedia. An encyclopedia entry on King George III would never be as comprehensive or as good a source as a biography. The encyclopedia isn't bad, it's just not supposed to go into that much depth. Its focus is instead breadth. Wikipedia is a great starting point, but for a solid understanding of the subject, biography or not, you need to crack open a real book. Both have their place, and I'd say are good complements.
We still need biographies. Wikipedia is not reliable and there are a lot of false facts on that website. Anyone can make an account and change or adjust information on Wikipedia. A biography is much more reliable that Wikipedia. It still amazes me that people read Wikipedia and just assume everything is true.
Although Wikipedia is an awesome source to gain instant access to information regarding a plethora of individuals, it is not the end all be all of information. The idea that one source should replace other sources for information is not a good one. The more sources there are to gain knowledge is the greater the chance the information received is the most accurate.