I've never bothered to carefully read the licence agreement... but it really comes down to how it is worded. If we are purchasing the software, then it almost certainly illegal to not allow us to sell or transfer the software. If on the other hand, we are only purchasing a license to use the software, then it really comes down to how the license is worded. In either case, until someone challenges it, it will probably just stay as is. As far as "industry standard practice" you definitely cant say that is true.. but I'm sure you can probably find a few examples out there of other companies doing it.