synfresh: A rental implies that at some point I'll have to return the games that I have. So please inform me when I will be returning my games to Steam and if you please, have some facts to back it up.
Ownership means I still own the product even if (among other things) the retailer runs out of business.
If Steam ever runs out of business there is no guarantee that I will be able to play my Steam games anymore. It's a possibility (them removing the DRM beforehand) but it is not a guarantee and as such there exists a scenario where I can be denied the enjoyment of a product I paid for even though I nominally would still "own"* it.
As long as such a scenario exists I cannot be said to own said product and thus the best it can be is a long term rental.
For a rental it's a good deal (at the right price) compared with returning it after a few days but a years long rental is still a rental.
You're of course free to view such an arrangement as ownership, just like I am free to view is as a rental, I just hope for your sake that Steam goes out of business after you die (hopefully of old age after a fulfilling life :)) or that they eventually drop DRM (like Apple did for music) before that.
BTW, the same goes for me as I have Steam games too.
* Technically we own licenses to it.