I've got a S8, so it might be a little different, but as far as i can tell there shouldn't be a difference.

Why is the bottom hose just a single elbow?

http://cgi.ebay.com/ebaymotors/Mazda...Q5fAccessories

The stock hose is more or less two of the elbows connected.

Eg, as far as i can tell, it should be like this: http://ricshawracing.com/wp-content/...8/DSCN2417.JPG

but the kits everywhere have that shorter pipe, why?

 

The stock intercooler has a bend right off the bottom of it, thus you only need the 'single elbow' as you call it for everything to fit.

Some aftermarket ICs (like ARC) have the inlet and outlet coming straight out of the top and bottom of the core, thus the bottom pipe has a pair of bends, and is shaped like an 'S.'

 

I've got a picture of my current smic bottom hose, apologies for the quality:



You can see the hose has two elbows in it, just like the hose on the left in this pic: http://ricshawracing.com/wp-content/...8/DSCN2417.JPG

also in this picture, on the left, you can see the stock cooler and hoses:


So what exactly are you supposed to do with the single elbow silicone hose they give you in the ebay kit above?

 

Never mind I worked it out, the earlier versions got 2 peice bottom hoses, later ones got 1 piece