Oh, gosh, I don't think Russell Group matters in the slightest!
8 years feels recent to me, because (like you) my reaction was 'huh, didn't know it wasn't already'.
My intention in pointing out it's a fairly recent addition is more to indicate that this isn't the most helpful way to view universities.
It's a tricky issue, in that xenia is right that prestige sometimes counts for more than the actual quality of the undergrad experience. It makes me cross, but I know perfectly well that there are universities that provide excellent undergrad degrees, but which employers get snooty about. And then there are also places that coast along on their reputations a bit.
But, I would say, if you're a student looking to study English, then the first thing to do is to think about what sort of course you want to do, and then think about whether it matters to you that this university is prestigious, or whatever else. There is absolutely no point in going to Fancypants Uni of the Year, only to discover you absolutely hate 90% of the syllabus and can't cope with the model of assessment, because unless you are incredibly determined and brilliant, you will end up doing much less well than you should.
I think this is very different from degrees that are more directly vocational (eg., medicine), because there the syllabus is pretty tightly linked to the job, and you'll have a more similar experience wherever you go.