If made well, often a WP app will run on W8 by just doing layouts with binding's to right data and calling your functions from event-handlers. Your app will work way better as a tablet app if you do not re-use the whole phone UI (you can still re-use some components / user controls).Why wasn't this the goal from the start? If they had one OS across all their platforms, all apps only required minimal modification to run on the different platforms (or non at all considering most development now includes a mobile version of the app) they would really gain some momentum. Their fragmentation makes android look like a dream! **As Ballmer cried about fragmentation in the android market.
Script kiddies really shouldn't try to respond on the technical side, sorry.I know the reason I never thought about buying Windows RT is because its redundant. I think its entirely possible to do this outside of games. The C# implementation can make it simple to compile programs for all Windows Devices. The exception is of course high end games that require the more powerful C++ code.