For the Guardian, the "horse has bolted" in terms of introducing a paywall he said, speaking at the Digital Media Strategies following a speech by News UK's chief executive Mike Darcey.
"If we could do a paywall of course we’d do it," Miller said, "we’d love to, but that horse has bolted".
Instead, he added, "membership to me is adding value". Asked for more details on how such a model might look, he responded: "We’d have to find out in coming months".
But, he added, "we’ll make sure we're offering services that add value to [members]".
Responding to questions raised by Darcey over the long-term sustainability of the Guardian model, Miller said "the idea that this is a model that doesn’t work is crazy, it’s working".
Just yesterday the Guardian reported a 25 per cent rise in digital revenues to "around £70 million".
But Darcey had challenged their model of having a paid-for print product, but free content online.
While he identified "some big positives about their approach", in terms of its wider journalistic aims, he questioned "how will this pay for itself in the long run".
He also questioned whether the global nature of the Guardian's operations will "one day be large enough to fund professional journalism".
"It hasn’t happened yet," he said, stressing that it is "still a heavily loss-making enterprise".
"[That] might be fine for the Guardian at least for a while, but it wouldn’t work for me."
But, Miller responded, during his speech, "yes we're loss-making but we’re in good company".
One particular subject raised by Miller was the Guardian's approach of branching out across the world, in light of its launch in the US, and most recently Australia.
According to figures he shared with delegates, the news outlet has 90 million uniques worldwide, includng 23 million in the US and 3.8 million in Australia.
"The idea of UK being a state that can sustain quality news is long gone," he said, adding that this market is a "wonderful opportunity, rather than something to ignore."
Work with the open web
Miller warned people not to "equate open with free", the Guardian's focus is on operating within the free web, he said, to "follow the consumer" and respond to the way people are finding and accessing news.
"The reality of the world is that people snack," he said, and the Guardian approach is to "build a business around that", he added.
"Open isn’t a luxury... It's the way the web works, We're working with it."
And he argued against the fact that not having a paywall means you cannot garner high levels on engagement with readers.
The "myth" that news outlets "only get decent engagement behind a paywall is rubbish", he said.
And working in the open web means working with different players who are ultimately helping to send traffic their way. Sharing live data from within Guardian's Ophan analytics platform, Miller showed referrals from Google, Facebook, Twitter, Reddit, Drudge Report and others.
"These aren’t our enemies, these are our friends," he said, and newsrooms like the Guardian "have to embrace them".
Not to do so would mean a "story dies very quickly", he said, adding that it is "essential to our business model to ensure our journalism is read".
"This isn’t about trying to protect old business models. It is about how the web works."
Different paths, same confidence
Both Miller and Darcey outlined their contrasting approaches and similarities in terms of their wider ambitions to support professional journalism.
And both were, unsurprisingly, full of confidence as to what the future holds but Miller stressed that different models will work for different outlets.
"News organisations of quality will win out in the end," he said.
For the Guardian it is "all about getting a large audience, increasing loyalty and revenue", he added, referencing recent figures which he said showed a 5 per cent increase in net revenue.
Darcy added that as well as wanting News UK to "win the market", he also has "a broader interest in the success of the category".
"In the end everyone will make their own choices and we’ll see how it goes".