Some buy fancy pants cameras in the belief that they will get 'better' photos from them. They might get more megapixels and a bigger sensor, but the money is usually about the bells and whistles.
A professional may buy a more expensive DSLR as it gives them greater flexibility, not because they produce a better image than one that costs £1000 less.
When it comes to the lens, you buy what you need. If you are shooting landscapes or portraits or gig photos, whatever. You buy accordingly. Unless you are very fussy, or a professional who does require top notch quality, you don't need to buy top end.
I consider light and composition to be the most important aspects in photography. Most of the photos I have seen and love have come from bog standard compacts.
The trouble is, I've found, when you start looking into buying a new camera it's easy to get wrapped up in all the details of what this camera has or hasn't got on it etc and you can begin to miss the point. I had no need to buy my D90, for example, I wish I never had.
Anybody who says they need an expensive DSLR in order to take effective, interesting or 'pleasing' shots isn't a good photographer in my opinion.