I don't think you made a mistake.
OCZ and others are using 25nm memory in place of the 34nm now that it's available.
The rated life span is shorter, and thus more "unusable" space needs to be allocated in order to maintain the system rated life.
So the formerly 128GB drive is now 120GB.
In reality, you will replace this drive long before it wears out.
I don't need to redo the pro's and con's here. You can read all about it in the OCZ support section of their website.
They are very up front and honest about this.
The big advantage you already noticed is that the price is lower. The newer memory is cheaper to make, so you save $$$.