> And that forum also provides an enormous amount of value to a company, saving them many multiples of that cost in reduced support expenses.

The calculus has changed a bit. They are losing sales from people using older versions of the software that they wouldn't have provided support for anyways. In Adobe's mindset, for example, Photoshop CS6 is the poison that is holding back subscription sales, not their competitors. So an easy way to frustrate users into subscribing to the latest version... delete the old forum posts!