PhotoShop may be the oldest program running on your computer now. The fact that there's even a modicum of commonality in the UI is amazing. While I agree that there's a lot of room for improvement, anyone working who's ever touched legacy code can see that there's more to this issue.
He's defending PSD by saying "It works great the way it is. And people shouldn't be wanting interoperability with Photoshop.
A key phrase is "And it's not at all clear that the benefits here would outweigh the costs.". Whose costs, and whose benefits? Obviously it wouldn't be great for Adobe to have to re-write their file format, and they wouldn't get that many happy customers initially.
http://blogs.adobe.com/jnack/2009/05/some_thoughts_about_psd...