No, Wind and Mobilicity are not stupid. You can browse and check your email, but do you really think they are going to let people do heavy gaming, downloading torrents, etc.? They throttle, cap, block ports, etc.This is why Wind's model is non-viable. Same cost of customer acquisition as the Big 3, half the ARPU and network load that will creep up higher as customers offload all their data usage to the cell network instead of fixed line networks because of a $25/month flat fee.
If you want a full internet solution you can get a USB Wi/Fi thumb from them pretty cheap anyways...
Tethering is just for people that want to browse/email and download the occasional program file, not for all out multimedia/streaming, etc. Try it for yourself and see what I mean.