A QBs lost fumbles don't count against their passer rating.
Lost fumbles are a small percentage of QB plays. So small, that, when you include lost fumbles and treat them as INT, it makes very little difference in the rankings. A couple of years ago, I took the top 10 QB with at least 1800 attempts at the time, and compared their ratings late in close losses from 2010-13.
First, here they are ranked by pass rating. That's just TD, INT, completions, and yards.
Player...Att/TD%/Int%/YPA/Rtg
Romo ..... 222 / 5.0 / 4.5 / 7.8 / 83.1
Rodgers...136 / 2.2 / 1.5 / 7.0 / 83.1
Roethbgr..136 / 4.4 / 2.9 / 7.0 / 77.9
Brees ......142 / 3.5 / 4.9 / 6.9 / 66.7
Stafford....201 / 3.0 / 3.0 / 5.9 / 63.2
Ryan........196 / 0.5 / 3.6 / 6.1 / 58.8
PManning.. 94 / 3.2 / 7.4 / 6.4 / 57.3
Brady........162 / 3.1 / 4.3 / 5.7 / 56.6
EManning. 116 / 5.2 / 7.8 / 6.8 / 53.2
Rivers...... 232 / 0.4 / 6.5 / 5.9 / 44.7
This adjusted rating that follows uses dropbacks instead of attempts, and includes all QB turnovers -- treating lost fumbles as INT. Note that there is no change in the order of the rankings.
Player...Dpbk/TD%/TO%/Sk%/YPD/Rtg
Romo ..... 230 / 4.8 / 5.2 / 3.5 / 7.6 / 76.7
Rodgers...151 / 2.0 / 1.3 /10.1/ 6.3 / 75.1
Roethbgr..152 / 3.9 / 3.3 /10.5/ 6.3 / 67.2
Brees ......150 / 3.3 / 4.7 / 5.3 / 6.5 / 63.2
Stafford....215 / 2.8 / 3.3 / 6.5 / 5.5 / 57.2
Ryan........204 / 0.5 / 4.4 / 3.9 / 5.8 / 52.5
PManning.. 96 / 3.2 / 7.3 / 2.1 / 6.3 / 56.2
Brady........170 / 2.9 / 4.1 / 4.7 / 5.4 / 54.0
EManning 123 / 4.9 / 7.3 / 5.7 / 6.4 / 50.3
Rivers...... 252 / 0.4 / 7.5 / 7.9 / 5.4 / 34.7