Linden Lab, the folks behind the curtains of Second Life assert that you retain ownership to your intellectual property. Basically the laws that govern your ownership of it, continue to operate as they would anywhere else. No real difference there. The expression of that as data in whatever form it lives in Linden Lab's databases belongs to Linden Lab - one of those legal necessities to make the service go (if they can't legally replicate and distribute your data, nobody can see it), and to protect them from liability if they lose a row, or a file, or a RAID array eats itself.
There is an unusual little clause in the terms of service that grants a perpetual license to Linden Lab and to every other Second Life user (registered accounts are called 'residents', regardless of payment status) to any patent that you use as part of the Second Life service. It's in plain print, but you'd be surprised at how many people don't read that. We don't quite understand why that clause is there, other than to prevent classic submarine patents generating lawsuits on someone else's pre-existing ideas.
All in all, the real legal system you and I live under never ceases to apply to us and our actions just because we're doing something in a virtual world, on the Web, over a telephone, or in person.
That brings us to the last major 'ownership' item: virtual land - which while the terms own/purchase/sell are commonly used is technically a metaphor for the leasing of server capacity. That seems to be where we got into trouble.
If you are leasing something under conditions, that's a whole lot different to owning something (even ownership under a covenant). If you're leasing something, you can be cut off from it by the terms of the lease. Depriving someone of access to owned property though requires specific due process.
In the case of Bragg vs Linden Lab and Philip Rosedale, Pennsylvania lawyer Marc Bragg asserted that he thought he owned the property that he was deprived of when Linden Lab banned him for an alleged exploitation of the system.
Regardless of Bragg's innocence or guilt in that matter, if he had reasonable cause to believe that he had ownership of the virtual property, then Linden Lab had no right to terminate his access to that Second Life property without due legal process. If he was leasing, then things leaned more towards Linden Lab's right to terminate Bragg's service.
All of it came down to arguments about representations (and misrepresentations). It's likely no coincidence that the wording on the website started to strip out the word 'owned' just prior to Linden Lab settling out of court with Marc Bragg.
That, ultimately seems to be the prima facie explanation for the change in wording in the core Second Life descriptors. At present, no other explanation makes sense, but Linden Lab is not talking about the change in wording, or why it has been made.