Ok so..it seems that on my sent, i have 27 dex which gives me a +8. When i equip Mandalorian assault armor with a max dex bonus of +0 and a random blaster rifle with no +attack modifiers it looks like my atk modifier stays put. And on the character page it says i have +0 on Dex but the number is orange and not red, so im guessing only defense is only affected by this. And with the heavy armor on my defense is actually quite high since it gives like +13 defense which makes up for the loss of defense dedicated dex bonus. Further evidence supported by using master valor and while my defense was unmoved, my attack modifier while carrying a blaster increased! So really the ONLY thing you are sacrificing while wearing heavy armor is some powers and your defense modifier from dexterity. So for everyone worried about using heavy armor for blaster wielding bad asses, fear no more!
On a side note, anyone know if dueling affects Blaster "Rifles"?
Edit: Dueling works with blaster rifles