It is most likely a combination of both factors. If you do a little research for interviews with Linden Lab representative on the issue, you will often see mentions to corporate clients, universities etc. Those institutions traditionally have a rather low tolerance for anything which can be called "adult" content. Business is puritan (at least on the outside). This tactic seems plausible to me. I am just not sure, if business use of Second Life is really such a huge market as Linden Lab would like it to be.

Additionally, legislators are increasingly interested in "adult" content on the internet. This is by popular demand, probably .. an attempt to soothe voters. Many older voters consider the internet the epitome of "new" technology (which they do not need/want themselves) and the cause of many unpleasant changes in the society - especially youth culture.

A good example for this is the German government's latest move to install a comprehensive censoring system (like in China), which is only intended to prevent "accidental access to child porn", if course ;-) I guess we all know, what other purposes this system will find within a few years. But it is hard to appose anything where the published purpose is to protect the innocent children ...

Linden Lab is trying to get out of the line of fire with the new policy, which seems especially important as the press still over-emphasizes the sexual aspects of SL in an attempt to create more "juicy" articles and headlines. It remains to be seen of this tactic works. Short term there is a renewed wave of press coverage associating Second Life with sex BECAUSE of the policy change. I have even read some articles spinning the creating of a "red light district" as an attempt to ATTRACT people looking for sexual content. :)