Don't need to be re-written, they just need a new ui layer. Take adobe for example, photoshop is not written in .net for windows and Xcode for mac. It's written in c++ for both with largely the same code for both. Windows 8 supports c++ for metro, apple only support objective c for iPad. So your right the iPad does not have complete photoshop but there's also bigger reasons why it doesn't over why a windows 8 tablet wouldn't.
Considering that Adobe has not found a way to integrate their UI across all programs successfully within their Suite on either OSX or Windows, I find it hard to believe they will be able to do so specifically for Win8 Surface.
Also... I truly find it hard to fathom that Win8 Surface fans will pony up for another license to run Photoshop or any other CS6 program on the Win8 Surface.
Or will the Surface be "enough" computer to disable the license on their desktop?
They will "purchase" another license at full-price, won't they?
Or at the very least from Adobe, purchase a monthly subscription.... right?
My skeptical side says "I just don't think so" to all of the above.
As a consultant to many photographers, I've also been witness to quite a phenomenon.
After integrating an iPad or 2 in their work flow and having access to some pretty powerful and easy Apps on the iPad, they ask me for equivalents on the desktop. On OSX, we've seen a number of initial iOS developers decide to port their offerings "back" to OSX.... and in many ways, offer a far easier approach to effects, filters, etc. than a full version of Photoshop.
If developers are not "prodded" to think different about touch, power-conservation, etc... will they?
Will there even be developers that come out with innovative easy-to-use Metro apps, and be requested by their fans to go "pro" with the same ease of use and concept, as we've witnessed with iOS->OSX?
Let's also not forget, that some of the power of Photoshop lies in it's 3rd-party plug-in developers. Considering that Adobe advises to disable 3rd-party plugins when troubleshooting problems, and this will be no different on the Surface... how is that going to effect the "run anywhere" approach Microsoft is taking? And believe me, plug-ins are very often the culprit... so are THEY going to also rework their add-on software to work on the Surface?
Also... what about device and graphic drivers?
Yes I realize that supposedly, the Surface will be basically a touch-enabled netbook or even notebook. However, I think anybody that has ever seen or tried a so-called "pro" program on current devices (other than an MBA), knows that there are some serious compromises they will have to make to call it "pro" in every day or even casual usage. Please see my initial statements above and ask yourself, "will it be worth a license"? Really?
Color me VERY skeptical that Microsoft Surface will be releasing anything approaching the power of an MBA... and again, at what price-point if they do?
Developing specifically for Metro or for the Surface Pro, could be a costly mistake at this point in time for any developer, both small and large.
So we're back to the "horse-cart" and "chicken-egg" conundrum: without certain developers on board from day one, Win8 Surface RT sales will go nowhere.... and without a Surface Pro to test or develop for, there will be no "new", innovative, or optimized apps.
As a betting kind of guy, my wager is that WinSurfRT won't get off the ground in any serious numbers, and that a working* version of WinSurfPro won't be available until Summer 2013.
*The first batch will have all manner of problems... but Microsoft WILL keep trying, that's why I don't think they will kill it. Trends point to the fact that they can't afford to give up. MS will be the next "rags to riches" tech story ~ 2015.