After all, this doesn't prevent people from NOT upgrading, it just prevents them from un-upgrading. It adds the ability for the company to release whatever they want as the "last" upgrade and be sure that no one (of ordinary consumers) would be able to undo it. That last upgrade COULD be wondrous and happy...or it could be a massive degradation of performance. In the former case, there's not much of an argument for forcing people to be unable to leave it. But effort was expended to make that the case, so planned obsolescence seems a reasonable conclusion.
More generically, this feature exists so the company can change the product after you purchase it and you can't undo that change. Planned obsolescence is your product not longer working "as well" as it did initially, forcing a replacement. Those concepts seem awfully close.