development resolution

In the past I beleive there was only one resolution for iDevice development and that was 480x320. The iPad added a new resolution to develop for which are usually the "HD" versions of apps.

How exactly are the new iPhone 4 and iPod Touch 4 devices going to be developed for? If 960x640 is used will this be a special HD version that will only work on those devices sort of like the "HD" version for the iPad or will older ios devices downscale a 960x640 app to 480x320? I beleive older or current apps developed for 480x320 will automatically work on the newer resolition ios devices but what about the other way?

Will there now be a standard, HD and almost HD version of apps?

Thanks for your help. I have just started exploring moving over from a Flash and Director based development world into an ios world so I am new and learning about Objective C. I read a lot of documents that talk about the 480x320 ios devices but nothing about the new resolutions.

 

But what has to be done to support older devices if I were to create an app that used 960x640?

Also in theory shouldn't pixel doubled older apps look pretty much the same way they did on the older iDevices? After all the screen size itself is still 3.5" but the resolution is double. So if older apps are pixel doubled wouldn't they have the same pixel density as the older iDevices and look about the same?

I think I may have finally found the answer to my question although I'm not how accurate this article is.

http://www.teehanlax.com/blog/2010/06/09/designing-for-ios4s-screen-resolution/

It sounds like moving forward app developers who want to use 960x640 will have to make two sets of graphics. One to support the smaller standard and the new set to support the higher density displays. Seems like a lot of work and it makes sense now why a lot of app developers will still be using 480x320 for awhile yet.

Can anybody confirm if this is true or if there is some clever trick to make ios downscale for older devices?