I just talked to Spotify via Chat. They said it's considered a discounted plan because you can have 5 people on there ... which ... kind of makes sense. I disagree since I'm paying the whole bill and it's my wife and kids on it who don't pay me back for it :)
I agree; worst part is, their "support" is anything but. When you contact them via Twitter to express that it's absurd to offer this to less expensive plans and not the one you've been paying for, they direct you to post here instead of doing anything to fix it.
I've set a reminder to cancel my account the day before renewal, as I'm pretty dissatisfied with how they have handled this.