Well wouldn't disagree with you there John. I certainly found a great review of one below:
http://www.cloudynights.com/item.php?item_id=1438
Actually John, after reading further seems they use "special ED Glass" not specified as Lanthanum (as done in the XL or XW), assuming to keep costs down. This must effect something in some shape or way as you say. It's amazing how much extra weight and cost goes into the extra 5 or 10 degrees field (XL or XW) you must admit.