"How many businesses will revisit their iPhone support now that they know Apple shipped and promoted a product as fit for business only to later find that the device had a major security flaw? "

Probably not many. Many products, including ones never patched without a paid upgrade, have had known security flaws. Including products like Windows, Exchange and Office. Hasn't stopped their acceptance as industry standard tools has it? In terms of how it effects the iPhone enterprise user base we should consider a couple facts:

iPhone OS 3.0 was released at the same time as the iPhone 3GS hardware (June 19th 2009)

iPhone OS 2.x did not support Exchange.

So I think you can make a reasonable case that before June 19th 2009 very few of these encryption-required companies were buying iPhones since they simply didn't support Exchange. Post June 19th 2009 how many companies were buying non-GS models? We could further sub-divide this based on the discovery of the encryption loop hole which you would hope any of these encryption-required companies were aware of. So by my crude calculations I think there is probably a month period where companies may have been buying non-GS iPhones with an expectation of pure encryption-required support.