BOAC - Talking 737-400 here!
Provided V2 is above Vmca (bear in mind, as Vmcg is done on flying surfaces only, Vmca is probably going to be somewhere around Vmcg = 115/117 as applicable) and if you look at the speed card we have, the lowest rotate speed at 115 kt (no lower!) then the increase in engine power is not going to be an issue here! Given that the lowest V2 is 131, you should get an adequate margin of control!
Now why the V2 decreases I dunno - Bear in mind that a higher V2 gives a better climb (hence increased V2 climb out terrain limited places) I am struggling on that one!
Fernando - Was only talking about V1 in general terms, not increasing it! But having said that. Given a long enough runway (737 doesn't need much!) the ammount that you can reduce ceases to become balanced field based. Instead climb out performance (single engine/WAT limit) is the limiting factor. We don't aim to just crawl off every runway out there! So because you typically end up with a runway that is longer than you require, V1 will normally be the same as Vr. (Not always though!)
CCCccccccoug......h