You can have bad or good streaks.
I did 4 HM 55 FPs in a day with my guild on my scoundrel ( me being the only smuggler in group), where we got 8 elite smuggler drops. (I was fully geared after that
On the other hand, i have done 10-15 fps on my Powertech, and never seen a single Powertech tank drop.
Those are extreme examples, but with a system based on luck, you can get both extremes.