"but for informational sites, (like this one),"
And here I thought this was an entertainment site, like all the other red-tops.
"sponsorship of some kind is the only viable model as things stand."
It's only viable as long as the readers allow it. Marketing doesn't seem to grok that.
"I agree, we all hate obtrusive adverts, and everyone's opinion will vary, but blocking all adverts is not a sustainable policy in the long term."
It's perfectly sustainable by the only person who matters ... the reader. This is MY computer, not google's. I decide what is displayed, or not displayed, not google.
Consider that google could make it impossible to use their site when running ad blockers & script blockers ... but they don't. Ask yourself "why?".
Also consider that my 70+yo techno-phobe Mom discovered and installed Adblock Plus, Flashblock & NoScript all by herself, without any prompting by me, because as she put it "that stuff gets in the way when I'm looking for something". If my mom can do it, I suspect that there is a growing wave of people intentionally blocking advertising.
Does it make sites like ElReg unsustainable (assuming all or most revenue is from advertising)? In my mind, yes. That's why I sold off my own "portal" just before the dot-bomb crash (that and the fact that I was offered more than enough cash to retire on!). I suspect that at some point in the future, sites like ElReg will have to move to a subscription model and/or sell more merchandise in order to survive.
Even with a subscription+advertising model, it'll probably not be sustainable. Don't believe me? Look at AOL for a prime example. They had tens of millions of captive eyeballs PAYING (monthly!) to look at non-blockable advertising. Where are they now? They went to an advert-only driven model, and promptly started floundering. In a nutshell, people learn to ignore online ads out of reflex. AOL would have been better off being advert-free and a subscription model service.
Even google, with it's near monopoly on searches, is probably not sustainable (never mind their paper value at the moment). At some point, probably within 5 years, I'm betting that a hardware company will buy them out for their proprietary clustering technology, at which point the name google will fade into obscurity (although it might stay around as a verb for a few years).
Remember, the Web by it's very nature is ephemeral at best.