You people really do not get it do you? Adding Deathfield gives you more burst than a standard Deception spec. Period. Run the numbers yourself, any gear level. I'll try and lay it out. For this example, we'll say that Duplicity procs at a good time, and so did chain shock for both rotations.
Recklessness> DF> Discharge> 2x thrash> Shock + Chain shock proc> Maul
2x VS> Recklessness> Shock (with VS buff) + Chain shock proc> Discharge> Maul
Assuming that both rotations get the same number of crits, the 0/27/14 rotation will ALWAYS do more damage than the 2/31/8 rotation. The only time 2/31/8 will pull ahead is if the crit RNG isn't as nice to 0/27/14. Claws of Decay will usually put thrash's damage close enough to VS' damage.
It's a bit normal that it does higher damage if you add an ability in the rotation...
The 31pts-spec uses 5 hitters (2x Voltaic, Shock, Discharge, Maul) while the 27pts-spec uses 6 (the same 3 Force powers plus 2 Thrash plus Death Field).
If you want to compare properly, add a third Voltaic Slash at the end of the 31pts-spec's rotation (or Low Slash if in need to stop a guy and find a position for Maul or to interrupt him), so that both takes the same time to use (and note that if it's Voltaic slash, it means that while the 27pts-spec ends its burst, the 31pts-spec is already starting to build its next one).
I also hope for you that your Death Field hits only one person, or it will be hard to crit your Discharge/Shock.