I respectfully disagree with that. All WebMistress said about her/his onpage was that the keyword density increased- that's bogus. Keyword density is not a considerable factor anymore, and if that's the reason you seize upon then I have serious doubts about your on-page prowess (no disrespect intended).
Proximity to the top, bold, proper use of italics, h1, h2, proper use of css for unessential bold/italics, keywords used together and apart, location of links within the pages- all that goes into it.
If you're worrying about keyword density I would respectfully suggest to forget about it and to look into the other factors I named above instead.
It's like poker, you have to have the cards, onpage and offpage- different cards and combinations are worth more. PR doesn't matter as much anymore if you can hit the on-page factors in addition to the insite factors, and the link factors. Ok, it's a mouthful...