First of all, I fell asleep within the first 10 pages the four or five times I tried reading that book, so take this all with a grain of salt...
But there's a handy bitterness unit/gravity unit chart that you can find pretty easily online that shows the relationship between SG/OG and IBU and how the ratio affects the balance of sweet and bitterness and completely changes the flavor of a beer. If I read your question correctly, I would think that this is what he's talking about, versus hop utilization changing the IBUs themselves (see above comment, haven't made it that far so I don't really know what he's trying to say!).
From the example, though, if you were planning a 1.045 beer with 35IBU, that puts you solidly into the "extra hoppy" category of the chart. Drop your gravity down to 1.035 with the same IBU, and you'll have a beer that will likely be unpleasantly bitter, ie, no "malt backbone" to balance the bitterness of it.
Then again, he could be talking about something completely different.