You're probably right - but there are no lightweight 18s out there without spending an arm and a leg. The 17.2 lbs for the ASAs is actually quite amazing for $184 each. THe next lightest 17 in wheel were the OZ superlegeras at 17.1 lbs (only 0.1 lb difference) in size 17x7s - and only available in silver, not in the darker satin silver the ASAs were - PLUS they are a good $100 more per wheel - and a very similar disign.
I decide - quite rationally - not to drop $419 each on the SSRs or $519 each on the sweet looking grey BBS rims i posted above.
All in all 17 lbs. for 17 in. rims at $184 is a hell of a deal - I like the design, and couldn't care less the difference between 17s and 18s - I'm not going to be going nuts in the corners too often. Plus the tires would have cost me more for the 18 in 235/40/18s as well. Like $40 more a tire.
PS ... watch on eBay in the coming week or two for some 18 in. Vault Chromies with 225/40/18 Conti ExtremeContact Rubber.