Yeah, the two flatrate methods and weightquote are all labeled the same way because they all fulfill the same niche. The rates are all defined by the user, and because they are specified down to the product level, they are made to apply to all shipping types.

Shipping types are defined by shipping modules, and of all the ones that we have so far, only "small package" has been needed. A small package is basically anything you don't need a freight truck to move. Any reasonably sized box is accepted by UPS, FedEx, and the Postal Service, but for things like pallets or skids, you need to get a freight carrier. I've written a module to deal with freight shipments because we need it for our restaurant equipment site, but haven't released it because no one's expressed interest.

Shipping types really have more to do with order fulfillment than they do with generating a quote. I made the Shipping Settings page in anticipation of needing it, but haven't had anything to put there, yet. I need to look over where the various settings are being used and shuffle them around a little bit.

As for all the theoretical stuff, I'm not much help. We already had accounts with them, so I'm just doing what I'm told.