Well, I've played about 95 years now and almost always made the playoffs in some fashion and what I've found is that I will often win it all but there are times when I will lose to teams with far inferior records. With that being said I will win more often then I lose. Remember, this is a simulation and as such in based on probabilities. Now if you toss a coin 8 times in a row you might get 4 heads and 4 tails, or you might end up with all heads. In the long run you'll probably average around a 50/50 split but in the short term anything can happen; meaning you could easily lose 4 or 5 playoff series in a row. In the long run that won't be the case, but anything can happen short term. For example, one of my teams won a ridiculous 120 something games one year and then lost in the first round of the playoffs. Now if they'd played that team in a 100 short serious they'd win a lot more than 50%, maybe even as high as 80% or more. But again this is just a sample size of one and they lost. This is all just probabilities and you've had a bad run of luck.
Also, keep in mind that if you have the best team and won every year would that really be any fun?
Hope this helped a little.
Tarkus