But it's not. As far as I can work out, IPS is cheaper than vB, a lot cheaper. From what I can see on their website, all you get when purchasing a new license is a forum and a blog platform, and possibly some way to create articles. The price for that is $249, if you don't want support. That costs an additional $49 pr month, or $199 annual. One full year, with official support, adds up to $448.
IPS, with the forums, blogs and Pages (which I believe can't be compared with vB's "articles" at all) costs you $275, with the discount you get right now. This includes 6 months of official support, followed by a half-annual renewal fee of just $50. In a year the total is $325.
With those facts, how can you possibly state that vB is cheaper? If you want mobile support with vB, toss in another $150, plus a monthly $49 support fee. IPS has that built in with the responsive design, and they are considering apps for iOS and Android.
And lets say vB6 comes out in two months. That would cost you $199, just to upgrade your license. With IPS, you'd get that for free if your support subscription is active.
Even if you take the whole IPS Suite which gives you four additional official apps, the annual price is still way lower, $465 + $105.