Because it is a different platform. I can run my old Nintendo games on my XBox. That does not make my XBox a Nintendo, nor my Nintendo an XBox. It is something called emulation. Even though the processor is the same, the motherboard (and the BIOS(PC)/EFI(MAC) that interprets the instruction set of the processor) is different. Current Intel based Macs cannot run Windows or Windows programs natively. By the same token, OSX for Intel processors cannot be directly loaded onto PC machines without some hacking. And while the processors are the same, much of the hardware cannot be directly taken from a Mac and put into a PC (even if there is a corresponding slot and drivers). When, for example, ATI makes a video card for Mac and PC both, sometimes it is just the drivers (software that runs the card) that is different. Sometimes there is a physical difference that prevents you from using the PC card in a Mac or the Mac card in a PC. As I said, for the programs you have stated that you want to use on your notebook, the increase in time that it takes to process actions will most likely not be noticeable to you. Using Word is a lot different than using Photoshop with a 3600x3600 image (though in that case you could use the Mac version of Photoshop). There has been talk that future Macs may indeed allow you to run Windows natively, but not currently. The current version of Windows emulation on a Mac is far superior to what was available before (Virtual PC and the like) but for resource intensive applications it is not the same as running it natively. Since you won't be running those it makes little difference to you.