Did some napkin math since it was still bugging me heh...
With a set of gear I was testing with Mjol and WFS I was 9554 DPS.
So then I removed the proc effects from both trinkets. Now I show 9003 DPS.
Then I added the procs as static values to show what I would be with them proced and am at 10697 DPS.
Given that the two procs "should" line up exactly throughout the fight so my average DPS "should" be 9003*2/3+10697*1/3 = 9568 DPS.
That is assuming instant up and always in sync of course. Assuming only 30% up time instead of 33% gets you 9511 DPS.
So the net answer is that you are right. The approximation done in the modeling is good enough. It could be over valuing or under valuing but it's in the right ball park regardless. Chances are, actually, it's overvaluing. Only on the "perfect"
case of 33% and always lined up do you beat the listed DPS and then only barely. A couple percentage points off and you start to plummet.
Once you add in the ICC ring procs, berserking, various buffs that might be on or off at a given time, whether or not Bloodlust lines up with the procs...you're in the land of approximation anyhow I guess heh.