Judging by the success of the iPhone and iPod touch, the lack of Flash is certainly not going to be a significant negative factor. I would argue that other platforms inability to develop custom apps using Cocoa and the iPhone SDK is a significant drawback for the competition.
Also, having witnessed how Apple introduces and rolls out new products, like the iPhone, I expect to see new features announced on or about the day the iPad actually goes on sale. Could be a front-side camera, could be support for the background operation of 3rd party apps (beyond simple notification), or who knows what.
Further, referring to the iPad as “just a giant iTouch” is certainly missing out on some very differentiating factors. The new interface and interaction capabilities alone are significant, but then combine those with new microprocessor architecture, lower network pricing, and an expected partnership with old-school print media, and it’s increasingly difficult to bin this product into any of the established categories.