I felt moved to respond in this thread because the Wikipedia entry quoted here is (largely) my work.
I'm not particularly proud of it, for the reasons you'd expect: it is, by its nature, written in the deathly, sitting-on-fence style that Wikipedia requires ("widely felt to be", "both its supporters and its critics", "many people believe", "it has been claimed", etc). But I felt it needed to be there - in its own context, the claims which have been disputed here are the usual Wikipedia criteria of expressing opinions felt by a considerable number of people, not opinions which are being pushed or accelerated by the article itself.
The idea that, *with the same politics dominating the country as have done so in recent times*, an ITV dominated even by Thames - let alone LWT - would have been any different is errant nonsense. Granada had the most public-service, the least proto-Murdochian and quasi-American (in the sense that the latter term was used in the UK before HBO and modern US drama arrived), culture of any leading ITV company, and its journalism was the least uncritically pro-establishment in the way Tonight et al have generally been. But look at how profound and how total the culture change there was, even before its new franchise period had begun (David Plowright was forced out in February 1992 and Charles Allen in place by the end of that year). If a company as rooted in the "old" UK broadcasting values as Granada could transform itself for gain in the way it did, any company could have done (to some extent, you could say the same about the BBC as well). In all likelihood, a Thames which secured its new franchise term would have undergone a similar cultural shift within a matter of months. There would have been a total change of management and general priorities, and an overriding alteration of values and beliefs. As a company based in London, it would have had an overriding advantage in the first place, and consolidation might even have happened quicker. By the end of the 1990s, it would have been as unrecognisable from the company of old as Granada was. The name would have remained, but nothing else to speak of whatsoever. No doubt it would eventually have taken over production of Coronation Street from what had become its Northern base, a la the BBC's presence in Manchester - and that wouldn't have been much of a shift either, because Coronation Street in its latterday form is also wholly unconnected to the old Granada culture.
The idea that ITV would have been any different with LWT in control cannot even be sustained to that extent; that company was at the opposite end from Granada under the old system, far and away the most proto-Cowellite, the crassest, the most populist and market-led (at least by the 1980s, i.e. after the old establishment had finally seen off Lew Grade). The cultural shift required for an LWT-dominated ITV to become what ITV broadly did become would have been miniscule and tiny compared to the shift required for the Granada-led ITV - and if the latter could manage it, who on earth could possibly dispute that the former could have pulled off what would have been a remarkably quick and easy process by comparison? LWT unashamedly did all the stuff that you weren't supposed to do under the old order, but which became embedded and took root after deregulation - they took *pleasure* (see the great 'Running the Show' here) out of being the anti-Granada. (And the idea that Granada post-1992 had any meaningful connection left to the old company in terms of dourness and fear of pleasure, and that this was why latterday ITV supposedly didn't do light-ent properly, is even more bogus and nonsensical.)
The one thing that would have been required for a different broadcasting culture post-1990 is different politics post-1980, which depressingly and frustratingly rarely get discussed here (or in similar places). If you had had those politics, I don't at all rule out the belief that the expansion of technology and communications could have been harnessed and managed in a different way. But even attempting to invoke a different post-1991 ITV without also invoking a world where British and world politics did not take the turn they did is as pointless and naive as attempting to invoke, say, the continuation of European communism (or, perhaps, its becoming more liberal while western Europe became more socialist) without also invoking such a political difference.
Neither a TV Forum thread nor a Wikipedia entry - which, by its nature, is a disinterested description - get close to the heart of it all.