Not at all. The pressure guidlines for various categories are VERY rough guidlines.
Pressures have NOTHING to do with wind speed.
Pressure GRADIENTS (the difference in pressure across a given distance) cause a given wind speed. If the pressures around a storm aren't that high, then even if the pressures are very low in the storm, you won't have as much wind as you expect. Around Andrew, for example, the pressures were very high..thus with 922mb you had Cat 5 winds. During this eyewall replacement, the pressure gradient in the core of Rita has weakened, creating a broader windfield but with a lower maximum wind, despite the pressure being WELL below that of Andrew at landfall.
However, the very unfortunate myth that there is a specific, precise windspeed that must be associated with a given pressure has taken hold. Once of the main purveyors of this myth, incidentally, is a certain well known AccuWeather TV personality.
Well, it was just summarily dislodged from my not very scientific brain for good.