I'd say they repel especially in the case of the Wii, most Wii games are designed to be multiplayer and when people need to buy 4 wiimotes and then 4 nunchucks and then 4 more add ons to get the "best" experience with Wiisports 2 suddenly games that require all these add-ons don't look so attractive anymore.

Look for instance at all those past games that required peripherals like the N64 games that required a memory upgrade (starcraft 64 comes to mind) Sega CD, 32X games, and Super Nintendo Light gun only games. Remember how well those things didn't sell and how few games were released for them? People in general don't like paying extra money for attachments.

On the flip side peripherals can be great profit makers, controllers for instance have a wonderful retail markup.

i think it attracts them