You obviously weren't around for iPhone 1.0. The "development environment" there WAS a disaster. And the sales increased by an order of magnitude once developers were allowed to contribute. If Apple hadn't embraced developers the iPhone wouldn't have much market share right now.
They're in a worse spot with the tablet. They're coming from behind and competing against companies that have been adding touch capabilities to laptops for years. I don't doubt the product will be awesome and that I'll want one, but they'd better "have an app for that".
Yeah, the iPhone/disaster comment was just a toss in.
The iPhone survived the development mess at the beginning because it was mostly being compared to other phones and its beautifully integrated phone/iPod/web combination was a revelation. Apps for phones were not a priority for the vast majority of buyers two years ago. That being said, the healthy development environment and the existence of the App store has now become a top selling point for the iPhone. We have no argument there!
Certainly then, if this rumored device isn't running standard OSX or iPhone OS programs, it would be completely useless without a long run up for developers. Assuming it is going to go on sale this fall, my money is on it running one or the other of these well developed OSs for that exact reason.