I updated to Mavericks as soon as it became available on my 2012 13" rMBP. Everything is more responsive, especially noticeable in Safari, websites just pop open faster. Scrolling in theverge.com is way better. Out of curiosity I went to the Apple store to try the Haswell version myself. I agree the difference in smoothness is not that noticeable, after my Ivy Bridge 13" rMBP was upgraded to Mavericks. But I bought the Haswell anyway, went with the 8GB/256GB config.
Edit: just got done setting up Safari with my usual pages. the 2012 seriously lagged when resize the Safari window on my Yahoo page (MUCH worse than scrolling in theverge.com - I'm talking like half a second for the screen to catch up. It is hugely improved with the 2013.
I have 2012 13in rMBP i7 2.9 w 512SSD and I see no lag issues with Yahoo(thats my home page with ML or Mavericks)
I never go to Verge so can't test that.
What did you see on Yahoo's page??