Confused

Hi Flan,
I have a knittery question for you and whomever else might be reading this. Gracie and I are doing a mini KAL with a tank. It's got a nice big V at the neck and the usual ribbing around the bottom. For the past couple of days I've been pondering needle size and ribbing and have come out very flummoxed.

Ok, here are the two parts that form my befuddlement.
1. Ribbing makes the knitted fabric tighter. If you're just knitting along and then, using the same needles, start ribbing it will get tighter - hence the whole point of ribbing (besides having a life goal of driving me crazy).

2. Going down needle sizes bumps up gauge, creating a denser, tighter product. Messing with needle size, and therefore gauge, is usually intentional- bigger needles= bigger knitting & vice versa.

So... if ribbing makes something tighter AND smaller needles make something tighter WHY on EARTH are you supposed to use BOTH methods when doing the hem areas?? Ribbing alone seems sufficient, why do the seeming redundancy of downsizing needles as well??

The combination of the two seems to make the hems oddly out of proportion to the rest of the garment. If you do an entire sweater on size 8s, then do 2 inches of ribbing on size 6s doesn't it result in really tight hems, clinging to the stomach region - a region not particularly known for being flattered by close fitting garments?? I'm very confused by the combo of these two techniques and am considering heedlessly flouting them.