Peter,
I think the rib rack is a very important tool. When you lay the ribs flat on the grill, the smoke does not flow as well. Also very important, the fat drips off much better when the ribs are on their side <don't forget to turn them over> or hanging , if you're going to make that effort.
The Weber rib rack leans the ribs over about 30 degrees. My contention is that the straighter <upright> the better for uniform smoke and drip.
Much better to use the Weber rib rack than none at all. I've heard that Brinkman makes a more upright rack, I've still to check it out.
Let's face it, you've got to work pretty hard to screw up a smoke on the Weber, it's that good ! but details is what all our fun is about.
Also, Yes you can fit more racks in the Weber when you use racks. As more and more people taste your ribs, you'll find that doing more in one smoke is huge. I've got friends, neigbors and co-workers now begging me for ribs.
Cheers!
Marc