Threadless vs Adjustable Stems/headsets?

[summerdays]

I know there are the 2 different types and that older bikes and the cheaper end of current bikes seem to have adjustable stems... whereas more expensive ones go for threadless instead.

But what is the advantage of the threadless ones ... since they are harder to adjust in height? Although I have just noticed on another thread that you can get Aheadstem Raiser to raise the height of the handlebars up (thanks kyuss).

And why can you pay vast sums of money for one ... ? what is the difference between one costing £20 and £200? (apart from the bigger hole in your pocket?)

(Sorry if I haven't quite used the right terms but this is one bit of the bike that I still don't really understand).

 

[skwerl]

the bearings are very easy to adjust and generally won't come loose over time. they're simpler than headsets used with quill stems too. The stems are much lighter and better at load-bearing around the steerer tube. They tend to be stiffer also
reason why they can be expensive is down to material (eg Titanium, Carbon etc), low weight etc