Firstly, he draws a clear distinction between a news outlet which claims to provide trusted reporting and the internet in general, where there is no implied trust (although Leveson uses the term ethical rather than trusted, which in this particular case I believe are interchangeable as trust in news output flows from ethical journalism).
Chapter 7, section 3.2:
"... the internet does not claim to operate by any particular ethical standards, still less high ones. Some have called it a ‘wild west’ but I would prefer to use the term ‘ethical vacuum’. This is not to say for one moment that everything on the internet is therefore unethical. That would be a gross mischaracterisation of the work of very many bloggers and websites which should rightly and fairly be characterised as valuable and professional. The point I am making is a more modest one, namely that the internet does not claim to operate by express ethical standards, so that bloggers and others may, if they choose, act with impunity."Leveson doesn't say this but there is also a jurisdiction issue online. It's not strictly true that bloggers may act with impunity if based in the UK, as there's always the possibility they will be traced using existing legal instruments and prosecuted or face civil proceedings for libel or privacy breach.
"The press, on the other hand, does claim to operate by and adhere to an ethical code of conduct. Publishers of newspapers will be (or, at least, are far more likely to be) far more heavily resourced than most, if not all, bloggers and websites that report news (as opposed to search engines that direct those on line to different sites). Newspapers, through whichever medium they are delivered, purport to offer a quality product in all senses of that term."Secondly, he draws a distinction between content being available (to those who search out such information) and being actively promoted, e.g. on the front page of a tabloid:
"There is a qualitative difference between photographs being available online and being displayed, or blazoned, on the front page of a newspaper such as The Sun. The fact of publication in a mass circulation newspaper multiplies and magnifies the intrusion, not simply because more people will be viewing the images, but also because more people will be talking about them. Thus, the fact of publication inflates the apparent newsworthiness of the photographs by placing them more firmly within the public domain and at the top of the news agenda."This I feel is a crucial point often overlooked when talking about privacy and defamation in an online context. Just because someone tweeted something doesn't mean anyone read it.
Having said all this I do feel Leveson is brushing over the effect of e.g. high profile tweeters, but it takes time and patience to feed an elephant.