That's actually what I believe. A (single player) game is a product. If you buy it, you own it, just like a movie or a CD.
On the other hand, an online game is a service, and the company asking for registration or setting other conditions on the customer is perfectly legitimate. It's an at-will situation...
I tend to agree, however that's not what the companies who actually publish Movies, Music and Games think. As often discussed, it's a growing trend to see an EULA attached to something you buy. This allows the Movie, Music or Game in question to be treated as a licenced product rather than a purchased one; you don't buy the thing, you buy a licence to use that thing.
Publishers are allowed to charge you for additional copies of a Game because they treat it like a product, however they then treat that same product as a licence by preventing you from doing with it as you please (such as installing it on multiple computers or not playing it online). This kind of thinking, which is entirely unethical, will soon become international law with the ACT Agreement, which is being negotiated between Copyright Holders and the Governments of the World and is being kept from public viewing because its considered a matter of National Security.
To sum up the Copyright Holders basic position for the ACTA:
You can buy something, but it is not yours - you've just licenced it from the people you paid. Because its not yours, you have to use it like you're told to use it and are not allowed to use it in any other way. If the people you bought it from stop it from working, because its theirs, you can't do something to then make it work, and you're not allowed a refund. If the product only works some of the time, you can't complain because its not yours, and you're not allowed a refund. The Government or Utility providers, like an Internet Service Provider, are allowed to look through your house and devices that are needed to use whatever it is you've bought to make sure you're using it the way you're told to use it. However if this thing becomes broken and needs replacing, well then its actually yours and not theirs and so you need to buy another one, and you're not allowed a refund for the broken one. Oh, and disagreeing with any of this is illegal.