STR makes your nuke weaker?

Hi all, I'm new to the forum, and I look forward to be part of this community
I was wondering about the INT and STR blues that can be added onto equipments. I find that often times people look for equip w/ STR AND INT. But, from my experience, if you're a pure build, the opposite blue only weakens your effect.
for example, i noticed that when i have equip w/ STR on it, my nuke dmg is weaker compared to when i take it off.
^(can somone confirm this? maybe it's just my imagination)
I don't understand why someone would strive so hard to remain a pure just to get equip w/ the opposite blue, isn't that the same thing as being a hybrid in a sense? http://forum.mmosite.com/topics/105/200711/20/3943,1.html?time=1208234461