lol, fight! I have to admit this one has got me going...
My argument would be that Nintendo games are, in the main, proper games. An escape from reality where you can enjoy yourself, they are not about fancy marketing, stupendously "good" graphics and impressing your mates, they are real honest to goodness games that put gameplay and having fun above all else. There seems to be a slowly growing shift in that direction too, against all odds the DS has performed despite the PSP and is posting some of the silliest sales figures I've ever known in gaming terms, you would be surprised at how many adults own them too.
The majority of UK adults follow the latest trend and are drawn in by huge marketing campaigns. If some of them actually sat down and played on a DS instead of a PSP for example, and didn't care what their mates thought etc etc, I think you would find that many would be converted within minutes.
You may not like them but dismiss them altogether because they are supposedly "kiddy" games is like dismissing classic Disney films because you've grown up. Having an open mind about such things had led to me discovering Hayao Miyazaki's movies, truely some of the greatest films I've ever seen...even if they are animated and generally feature children.