Protecting EoL questions because they're EoL would be fundamentally inconsistent with the purpose of protection in the Stack Exchange system. It also would not advance the spirit of our EoL-related policies. So while I agree that there are some not-very-good answers on that question (and some others), I don't think adopting a policy of protecting all old EoL questions would be effective or acceptable. Fortunately, there are some other effective solutions.
First of all, protecting a question does not prevent or discourage answers, except by very new (i.e., very low reputation) users. Even then, its purpose is only to discourage answers that are not really attempts to answer the question at all.
We want to keep it that way. If we started using protection as a way to discourage all or most new answers to questions--even symbolically, without changing the underlying system--then it would confuse and greatly damage people's understanding of what it means for a question to be protected. Most protected questions would suffer as a result, plus high-rep users would be reluctant to protect most questions that should be protected.
As a second and related, overlapping point, the official, SE-wide purpose of protecting questions is very limited:
Questions should be protected when they are garnering lots of views
and newbies are adding "me too!", "thanks!" and possibly even spam
Protecting questions to prevent people from posting answers that are actually attempts to answer the question would be a misuse of the system. Alternatively, it would be a radical change in the way the system is used, which is unlikely to be justified by the relatively small amount of harm that additional bad answers on EoL questions are likely to cause.
Third, it's true that we don't want new bad answers on EoL questions, just like we don't want them anywhere else. Bad answers should be downvoted (on EoL questions or elsewhere). Non-answer answers should be downvoted and flagged. Problem solved. But we do sometimes want new answers on EoL questions.
Often an EoL question--by which (in this context) I mean a question that is not eligible for closing, but would be if it were posted today, because it is about an EoL release--can be helpful to users of newer releases. Often they can be answered in ways that expand their relevance to currently supported releases. We want that.
Fourth, since EoL questions generally get fewer views and are less popular than questions about supported releases, they are, as a group, one of the least likely categories of questions to need protection.
Fifth, a review queue for late answers is not the problem here; it is the solution. Furthermore:
Running out of reviews on late answers is (1) not very common (unless you review an unusually large number of late answers, in which case, you rock and are awesome!), and (2) not really a big problem.
Even after you have exhausted your daily reviews in some category, you can still review in other categories, and you can still perform essentially identical activities by browsing through the site and helping tidy things up (by editing, flagging, commenting appropriately, etc.).
If you come upon a review item you don't want counted toward your daily review quota due to personal preferences, click Skip. If you want to edit or flag the item while still skipping it, you can browse to it through the link and edit it outside of review.
Also, I think that if we did protect old EoL questions, the question you linked to would still not be protected (or at least not as EoL). After all, it's only marginally an EoL question. There's nothing in the question or its accepted answer to suggest the problem is 11.10-specific.
With all that said, it might be worth investigating if this question should be considered a bug report. I suspect that it should not, but the described behavior seems bug-like, and if it is a bug report then it can simply be closed. As one of the short, late answers suggests, it may be Launchpad bug #854833.
We should not close all old EoL questions (only new EoL questions are off-topic for being about EoL releases, after all), but if there is another reason to close then we can go ahead. This question, even if closed, will not likely be deleted as a result, due to all the upvotes on the question and one of its answers. The best response here might be to close that particular question.
Finally, while being short and bad does not generally make something not-an-answer or mean it should be posted as a comment (related), I believe that particular answer really does not attempt to address the underlying issue in the question. I have commented to express that in slightly greater detail, and I have flagged that answer as "not an answer."