A marked difference is the inability to sell it to someone else or keep it for as long as you want for no additional price. The nice thing about owning a game is you get to play it whenever you want for any length of time you want. I have a decent backlog of games. Sometimes I want to play a certain game, sometimes I want to play a different game. Some years I will pay for an NHL game, and some I won't. I will keep the said game for a little bit, maybe sell it off later, or just play a game or two if I am feeling up to it. A subscription completely alienates me as a casual consumer.
Theoretically, but without knowing the price it is hard to say how much you would save on a per month basis (if at all). And if you do feel on a random month you want to play the game, I would have to resubscribe and pay a fee to play it for whatever amount of time I am wanting. So what if I have friends over after some time of not being subscribed to the game and we want to play a few NHL games? I have to pay a fee to play my game again? There is no allure in that for me.
If the subscription is less per year, then it may be worth it to hardcore players who get it every year, but they were getting the game every year any way.