The tablet pc pens were initially designed for resistive tablet PCs that require the two layers on the touchscreen to be pressed together for recognition, technology has moved on and the capacitive tablet pc has become mainstream, which does not use a touch pen. But the love for the touch pen has not died. Many touch screen tablet pc users still yearn for them, in particular artists and illustrators who like the use of pens over fingers because it helps them see the screen a lot better.
You should not be disappointed however, there are numerous pens that are designed to work on a capacitive touch screen, mainly because they have been developed to mimic the human finger [an impart factor because capacitive screen to not work on presses by conductivity of the finger]. Now you can carry on drawing with a stylus on your iPad without any worries, this is a welcome relief because artists felt left out when tablet PCs first started being produced without pens.