I have just stumbled across this website whilst doing a thesis. I have read in depth all of the information on here and I am afraid you are all right, and wrong. Everyone has a maximum heart rate and this cannot be exceeded, but it is the method by which the maximum heart rate is calculated that can be erroneous. Most people use a formula to predict their maximum heart rate (and there are several of these), whilst they can be accurate, there are also inaccuracies. The common methods are the "Tanaka, Monahan and Seals", which is 0.7 multiplied by your age, and this subtracted from 208 (so a 30 year old would be 208 -(0.7x30) = 187). The "Haskell and Fox" method is the most common (as it is the easiest to calculate), 220 minus your age. Therefore, 220-30 = 190.
None of these methods are used in sports science to determine a maximum heart rate, but they are useful to everyday sports people. It is possible that an individual may calculate their maximum heart rate from the formulae above, but using a heart rate monitor, exceed that figure. Equally, they may never reach that figure. The formulae work on the basis of averages, and there are many factors that can affect these.
The best way to find an accurate maximum heart rate (amongst other things) is to go to a sports science lab, such as Loughborough University, but this may be felt that is mainly beneficial for elite athletes. I have some links to heart rate specific websites and books, I will try to dig them out and post if I can.
I hope this helps you all. Regards, Steven.