you don't have to buy an apple display because the cheapest one is $700. an apple keyboard/mouse cost $49 each. thats $100. INCLUDING two lots of shipping and handling. so its probably more like $35 each.
A display is going to have a big impact on how you work. There are so many different types, values, qualities, etc. A keyboard is basically just a keyboard. Ok, a mouse is a little different, but who's gonna ship a keyboard an no mouse?
i think it comes down to this: I looked at the three "big" PC makers, and Apple.
Apple: default is a keyboard & optical mouse. $99 option for bluetooth.
HP: default is an "internet" keyboard, scroll mouse. $10 option for optical mouse, $50 option for wireless (doesn't specify what type) keyboard + wireless optical mouse.
Dell: You get no options. Standard dell mouse & keyboard. thats it.
IBM: default is a usb two-button scroll-wheel optical mouse, and "ibm preferred pro full-size keyboard". options: various combos of usb, optical, wheel for varying prices (i couldnt quite see the difference my self) various combos of pro, black, full-size & p/s2 keyboards. one "space-saver" model. again, differences not clear.
funny that. Not a single one offered an option not to have a keyboard or mouse. and all three companies are doing quite well. and all three no doubt have companies doing market research. im guessing they get very few people asking for the option to not have any sort of input devices at all.
at the end of the day, you could always go to some shonky PC shop, buy a $200 pc with no keyboard, but then you'd just come back and whine some more about how it won't run any of the cool software that apple makes, or runs on osx.