The article says ...at least as far as Web-browsing performance is concerned.. And this has already been discussed...the iPad 2 seems to be about 1.6x as fast in Javascript tests as the iPad 1 running the same iOS version.
To me, 1.6x is a pretty good increase and I wouldn't consider it "mostly unchanged". If a webpage takes 10 seconds to load on iPad 1, it will now take 6 seconds. If it takes 20 seconds, now it will take around 12 seconds. Pretty big difference, no?
And if you compare it to iPad 1 on 4.2.1 (which is what everyone was running, so it's relative to the end users experience), the iPad 2 is 4x as fast. So that same page that took 10 seconds now takes 2.5 seconds or the 20 second page, 4 seconds now.