According to a Nintendo UK representative, inclusion of a Wii Download Ticket number with Wii Speak microphone will in no way affect the ability for purchasers to resell the peripheral.
It was previously feared that the inclusion of the code, redeemable only once for the free Wii Speak Channel required to make use of the device, would prohibit purchasers of resold units from activating the device, but Nintendo explains that a new ticket number is just a phone call away.
"Any consumer who may have misplaced their Wii Download Ticket number for the Wii Speak Channel or require a new number following a Wii exchange may contact their local Nintendo Customer Services department, where they can request a replacement Wii Download Ticket number."
See? We were all worried about nothing. Nintendo obviously planned it this way all along, rather than simply reacting to the public outcry. That's just how they roll.
Nintendo clears up Wii Speak issue [Eurogamer]