It's more than one or two days earlier. And I also have it so I don't have to wait to order stuff until I have over $25 in merchandise. (If I wanted real "free" shipping, then that is what I would continue to do.) I certainly didn't pay the $80 for the crappy films they stream. It's simply a nice bonus to me. I wouldn't pay additional for it.
I'm thinking it was a poor guess, but who knows? I only know why I have Prime, and it's obviously not why you have Prime. I can't speak for the other 90% of Prime members.

In the UK, there is no minimum purchase requirement for SuperSaver, so Prime here really is just for impatient people. IMHO it's poor value for money anywhere, but moreso here since everything qualifies for SuperSaver. In the US you have to balance Prime costs against having to wait until you can meet the $25 minimum spend.

Mind you, there are plenty of crazy people with money to burn who pre-order stuff rather than wait for the inevitable - and often massive - price drops. Admittedly, again, such price drops are more common here than in the US: our starting RRP's tend to be higher but stuff gets discounted more and faster. But then over the last few years I have switched to sourcing a lot of stuff through the secondary market like MarketPlace. Why spend £12 on a pre-order for Iron Man when it will be selling for £1.50 six months later secondhand? Espescially as here in England there are several companies that specialise in buying up people's unwanted DVD/CD/games (for those who want to avoid the hassle of selling say on Ebay themselves). One is called MusicMagpie. They buy up DVD's and stuff often for pennies and then operate as a big seller on MarketPlace, selling for a pound (for really common titles like big blockbusters). Big profit for them, major bargains for me. Happiness.

The two-day thing is purely down to the fact that Sundays don't count as business days.

Here in the UK it is "working days" and Saturdays don't count either.

Amazon warehouse and fulfillment operations are continuous - 24 hours a day 7 days a week. It would be horribly inefficient to leave all that machinery and space idle for any time, they'd never keep up with orders anyway.

That's exactly right about the price drops and another reason Prime is nice in the States. If you wait for $25 bucks in orders those price drops can become price increases before you get a chance to order and you lose out on the deals. If you don't order often then Prime isn't price effective unless you like the streaming.

Amazon baffles me. I purchased a Kinect and Kinect mount for my TV. This is going to be a Christmas gift for my son. I have prime, but figured I am in no rush to get this, so I'll just pick the 3-5 day shipping to save them some money. What do they do? Send it via local delivery company today with delivery expected today. I ordered on Saturday. Now I do get they have a local warehouse here so that certainly may factor into their decision. Still weird to have them basically give me the same expedited shipping without choosing it.

I'm not on Prime anymore (haven't been buying enough for it to be worth it), but I did just place a pre-order for a few things that were promised on release-date if I paid for 2-day shipping. I did so, and not getting shipping confirmation the day before, I check the order and it says that I won't get the items until three days after their release date. I was able to cancel, but that's pretty shitty of them for saying they can get to me on release date and not follow through.