I can convert my entire wireless network and all its clients to WPA, including the PSP, but not the DS. Despite the poor uptake of WPA, there are competing products that do and don't offer it, so I can choose those that suit my needs. That isn't the case with the DS as many people chose to buy the system on the merits of its games, the way it should be. About the closest competition is the PSP, which does offer WPA. How will that look to people educated in the security of WiFi? How will it look if the DS is still using only WEP in even a couple years?
No signal booster necessary. A directional antenna will improve the signal exponentially. Even a weak signal outside your property can be used. And how about apartments? If you've setup a wireless network in one, you know just how badly the signals overlap and how many of those networks are left open (probably the best defense for your network, someone else leaving theirs open :¬]).
What is my problem is also Nintendo's. If they really want to see 90% adoption of their online service, they need to provide for anyone who wants to use it. They've made an easy-to-use adapter (and hidden it on their website....), they're providing free WiFi access at hotspots that would otherwise charge, and the service itself is free. But they choose to leave the security-concious out in the cold.
As far as the idiocy of selling the adapter through the website, while it won't stop someone who is net-savvy (oh how that word makes me cringe) from purchasing it, it will stop anyone who simply doesn't know about it. Are they going to stick an ad between the safety pamphlet and the game manual? Put ads in stores?... where it can't be purchased. I hope that this really is just a 'trial' and that they'll soon put them in stores too.