Iang27,
Personally I'd buy the 428XD over the 4280XD simply because of the PIP feature. I often watch one channel whilst waiting for something to come on, on another. PIP (picture in picture) saves you flicking about.
I think the main differences are PIP, more connections, the auto light level adjustment (the tv adjust according to the level of ambient light) and the ability to adjust the picture further (professional adjustment - although I'd never use this).
You need to check with the Pioneer web site for the exact differences though.
The reason why you have to travel to get the warranty is that its a condition that the dealer has demonstrated the set in store. Note the warranty offer is only until the 31st Jan so not long now.
I could have found a cheaper price but I was confortable buying where I did as they're a highly reputable store that I've dealt with for over 10 years. The bracket and warranty swung me along with the knowledge that I was saving over £300 on the cabling in the other deal. Otherwise it would have been the Panny.
I haven't got my system set up yet due to a few installation delays, however in the shop the 3500Se's sounded very clear. The non Se's are a lot cheaper around 1/2 the price but What HiFi say they're not as good. Without listening to them both side by side I couldn't really comment.
As for buying the speakers without the sub you'd have to look around but it could work out expensive. When sold together they come as a boxed package and often this is cheaper than buying them seperately as distinct speakers.
PS If you get the 3500's consider gloss black they're beautiful and match the 428. I got black speakers, black av stand then silver electronics and I think it looks great together. The black of speakers, screen and av stand compliment each other and the silver electronics just lift the blackness a little to give a touch of class.