I would argue that it is. What portion of iPad owners have ever spent any money on software or peripheral devices? Probably less than half. Now, what portion of them would be willing to shell out $50 for a stylus? I just can't imagine that a non-negligible proportion of iPad owners would be willing to spend that much on an accessory.
Also keep in mind that the current price point is "introductory" and will increase in the future.