The thing is, if everyone wanted to do this, which is making the phone sound like a desktop computer we would all probably be running Windows Mobile on our phones, the iphone doesn't down load attachment until you tell it, but thats probably because they don't wanna clog up the network which you gotta take into consideration, but it will check your mail and from what I know will refresh web pages when mobile safari isn't open. Spell checking a large text file on your phone? seriously? lol while editing photo's, well the only photo editing iv'e done on the iphone maybe takes a couple seconds to do, time it takes you to switch to another app, would be a waste of time switching which would then slow the background app dread to think if you was doing all those things how slow it would be, then you get a call and the phone crashes! lol
I tend to go with the less is sometimes more idea and we don't need our devices to do everything just because we can have the internet in a fridge do we want it, sometimes people have to know when to put the brakes on. I suppose it just boils down to people don't like apple or any company telling them they cant do things, but then you buy another companies product.
Rumours are the next OS update will bring multitasking but I'm not convinced, I think maybe when the phones are more powerful and has better battery life, but I suspect they will still want to implement it in a way so that people don't end up accidentally running loads of apps they didn't realise were still open.
I think there are a lot of Mac users that would agree, but like you point out the positives for the company, not necessarily for the users are big, they have a streamline product range, makes it easier in many ways. Easier to manage supply levels and much more. Plus they only cater for the high end market, not making cheap underpowered devices. I always remember going into the Sony store in Tottenham Court road and counting no less than 43 different laptop models in the Sony range, I think Apple being more specialised is to their benefit. Could be said the same for the iPhone, while every other company is busy churning out model after model, Apple has one model that just seems to work for a lot of people.