You are confused about the legal nature of a piece of property. Ownership of a physical piece of property has always been defined as a bundle of legal rights. For many, perhaps most items of property, that bundle of rights is all encompassing in the sense that you can do whatever you choose to do with that property. But for many items of physical property, the bundle of rights that are sold to you when you purchase the physical item are not all encompassing and never have been. If, for example, you were to purchase a nice piece of backwoods property in much of Appalachia, you had best check and make sure you are also purchasing the mineral rights to that land. In many cases, the ownership of the right to extract minerals has been split from the right to, say, build a house on the land. Similarly, in the American West, the purchase of land with a stream running through it does not automatically convey the right to use any of the water from that stream. The water rights have been unpackaged from the land ownership. This unbundling of land and water rights, in fact, goes all the way back to the Roman Empire.
The legal history of physical property ownership has been one where, over time, the bundle of rights sold with the property has been split into finer and finer bundles. DRM, DMCA, etc. are just a continuation of this trend. When Sony sells you a PS3, they have sold you a bundle of rights that includes some uses of that property, but excludes others. Sony is under no legal obligation to sell a complete set of rights when they hand over the PS3 in exchange for the customer's cash. If you don't like the exclusions in the bundle of rights Sony has sold you with the PS3, don't buy a PS3.
This unbundling of property rights is actually a good idea. If you were to force Sony to sell a complete set of rights as you seem to understand ownership, Sony would have to charge a higher price for the PS3. Since most people do not care to mod their PS3, removing that right from the bundle that is conveyed during a sale of a PS3 reduces the cost that most customers have to pay for the actual rights that they do care about.