The details are here http://www.flyforless.ca/news-westjet/westjet-news37.html
If that isn't nickel & diming, or bait and switch or whatever, I don't know what is.
They do still do seat numbers unlike SWA/Easyjet - don't understand why. Yes if you are flying long haul with a family you want to sit together, but a typical 1-2hour hop you just waste time getting up and down to let other people past. You still end up changing seats anyway as they shuffle people around to put families together or deal with unsuitable people in exit seats.
If you want the luxury of choosing a specific seat, you then have the option of paying an additional $10 to be assigned the specific seat that you so desperately need.
Other airlines do this too - it's not unique to WestJet.
To be honest, if the flight was less than about 2 hours i'd probably take my chances as I boarded. More than 2 hours and i'd happily pay $10 to get a decent seat.
There is no seat included in the price they originally quote you.