Yes I am. It’s definitely not there yet, but it’s starting to.
They have a choice, so does the other site you’re referring to, they just haven’t done it (yet). Wikipedia itself is a very large site, with lots of code, so a change wouldn’t be easy, nor would it really be worth it at this for what they are. Plus, search engines still have trouble with JS and still need at least fallbacks to get the data they need. If you disable JS on these forums you’ll see what I mean. (It actually looks a lot better than it used to, they added some CSS styling)
Meteor doesn’t have this server rendered fallback (or didn’t out of the box), the entire page was entirely rendered in JS. Up until the last year or so, Google listed nothing about the content when Meteor.com came up in the results. Just the URL. Now it has some basic info, but that looks like it might just be from meta tags. But, I don’t see that text in their meta tags, so who knows.
So, it’s still kind of irrelevant if you want your stuff to be easily indexed by search engines and don’t want to spend the time worrying about search engine versions. But, it’s heading that way.