Is it ?
Last time I looked it seemed to be you keep your current version, and just don't get newer updates if you stop the yearly fee.
If you keep being able to use the latest paid version, that doesn't sound as a subscription in my ears.
There have been times past weeks I have been tempted to get into Houdini, but life is getting in the way. I will be looking out for Igor's tutorial set, it might just push me over the edge.