I prefer user-experience and interaction which result in a good mood-, good conversation-, good content community, over SEO, and a few milliseconds of lag and advertisement impressions.
I know news sites that don't use ajax technology, because every page load is another ad impression. Not only that, they split their short article up over at least 3 pages.
What I would do is value the reader and take away that frustration. Offer a subtle advertisement that is worth something to them, have an organized one page article, and if there's rich media involved to not limit this to 200 pixels max but offer a great quality experience. If a company can spend so much money on trying to trick the user for ad impressions. They can spend that much money on the extra disk space and traffic as well.
Personally I rather sign up on a site where I don't get stuck in the account completion steps with required questions, extra captcha, avatar and signature management, and what not. All I want to do is drop a comment to participate in a great discussion.
I can't really justify sacrificing losing a good poster that feels welcome and was about to post on topic. Over a few milliseconds he or she wouldn't even realistically notice.
I am glad XenForo uses ajax where it's logical. Uses features to provoke positive participation. And uses third party services to connect users for a warm welcome.
What's next? Throttling their connection speed to guarantee a low average for all visitors, so the server load stays below a certain value? One rather has a slower browsing experience than a higher server load?
It's all a balance, and I for one am glad that XenForo has great features, understands social media and aggregates that data, and also syndicates it. A site shouldn't be limited to their url anymore, a site shouldn't be limited to their feature anymore, it's a platform, an interaction, it's part of a puzzle we know as the web.
In the example of Gravatar being unstable. It happens to me once on XenForo.com here the other month. For 12 minutes. That's once, since the first day I used gravatar ages ago. Not only that, as a user I can go to my profile and upload an avatar.