Very good point! While there is some variation in values (i.e. muscular people may tend to be heavier than "ideal" but have low body fat), the BMI chart and abdominal circumference measurements are 2 things that can help you determine if you are in a healthy weight range.
Abdominal fat (waist circumference) and "waist to hip ratios" are easily calculated. If you have a measuring tape at home, you can do this yourself. There are online calculators that will calculate your waist to hip ratio, you simply need to plug in your measurements.
Here is a website to get you started:
http://www.consumer.gov/weightloss/bmi.htm
Not matter what your weight, focus on being active and eating healthy. This is beneficial and still makes a difference no matter what weight you are at right now. If you stick with it, in most cases, at least *some* of the excess weight will come off. Even an 8 LBS weight loss has health benefits!
I agree that it is very confusing in this day and age to determine what exactly *is* a healthy weight anymore if the majority of people are above a healthy weight!