Don't worry yet. I will not be surprised if the MBA doesn't get updated tomorrow (whenever the MBPs get updated). Of course we all want them to be updated, but there's even speculation of no 13" MBP. The bottom line is only part of the information might have been released. Plus, the paper that called April 13th as the update day said MBP and MBA updates. In the past, we never got any information about MBAs when they were updated. Last June there wasn't a single rumor about its update.
However, I wonder if the reason here is either the graphics issue or the CPU shortages for ultraportables. I still think an MBA at WWDC makes a lot of sense as much as I don't want to wait. It just seems that Apple taking its time is probably a good thing. I don't want Apple to rush this and stick us with only Intel's GMA IGP - that would be devastating. Apple seems to have a bunch of updates coming this year... new LED ACD, new Macs all the way around probably including one graphics solution across the majority of the spectrum, new iPhone, new iPods, and maybe even another new product.
I say we wait and hope that if it comes tomorrow the MBA is better than the current model. Apple would be better off providing no update and just a 4 GB RAM spec bump with larger SSD and maybe glass trackpad than sticking us with a Core i5 ULV CPU and only Intel's GMA IGP. So I prefer we wait until it means we get the MBA we truly want/need.
I only want an MBA that's an improvement even if only the RAM we desperately need. On the other hand, wouldn't it be great to have an MBA that dominated the ultraportable market as the current v 2,1 MBA was when released in October 2008?