Header, Intake, & Exhaust - Difference in intakes

Ok everyone, whats the difference between these 30 dollar intakes you see on ebay and the 200 dollar aem intake. I know its supposed to be so much better, and everyone reccomends the aem intake, but is there really a difference? I dont see where a curved tube and air filter can be varied that much from company to company. Any info would be appreciated. BTW, sorry if there was already a post about this, i looked a few minutes and didnt find anything.....
Mike

Check this one. I't may help. (http://www.hondacivicforum.com/tm.asp?m=1972)