Heart Rate

Ok, let me see if I understand this. I'm a 27 yr old female, so my max heart rate is 199. This chart is from marathon guide.com

Zone 1 - Low Intensity zone: 50% - 60% of max 135-148
Zone 2 - Weight Control zone: 60% - 70% of max 148-161
Zone 3 - Aerobic zone: 70% - 80% of max 161-174
Zone 4 - Anaerobic zone: 80% - 90% of max 174-187
Zone 5 - Maximal zone: 90% - 100% of max 187-199

i don't get it... why would weight control be 148-161? Shouldn't it be higher?
I'm going to buy a heart rate monitor (yay gadgets!) but I don't really understand when it's good to be in which zone. what percentage of my workout should be in zone 4 or 5? or should I just stay in 3? Does it matter? is it better to just do the mileage, and not worry about the heart? am I overanalyzing AGAIN? ... not chandra, she never does that.

I'm getting annoyed at what the cold weather does to my skin. my fingers have been cracking and bleeding (with lotion on them!). *annoyed*

the chart posting didn't work. but i'm going to see "The Family Stone" after the gym trip tonight!

sweet.