Much as i don't like Mac's, these days they all run on regular intel hardware anyway, so if you want you can just buy a mac and add windows later if you want (on a dual-boot). Add to that the pretty decent emulation software you can get for Mac's so you can run MS Office. Having said that, open office is good, and Google are now offering free online office compatible sofware, which is good for occasional use.
Sure they cost a bit more, but the all in one design is pretty and OSX contains everything most non-gaming users need in a reliable and virus resistant form (if a little inflexible) Loads of creative industry types love macs, so photo, video, and sound software is readily available.
As ever with Apple, it's basically up to you if the high standard of design combined with their "closed ecosystem" thinking is worth the extra cash.
You can keep your internet provider, and dont need to change your external modem/router or anything like that. In fact, if you have an ethernet or wireless modem the most you'll need to do is type in your code for the wireless!