Re: Restrainable Limitation
All right, here is the 5E definition for Restrainable (p.200)
"A power with this -1/2 Limitation is generally by or based on an area of the body which can be restrained. Example include Flight defined as having wings or some HKAs defined as having claws. If that area or part of the body is Grabbed, Entagled, or otherwise restrained, the character cannot use the Power. When he breaks free or the restraint, or it is removed, the Power functions normally again"
Soooo....
Clovis: yes, most HA and HKA's should probably be 'Restrainable,' since they would require moving the requisite body part to use the power. However, a GM might allow some special effects to bypass this (say, and ED HA 'Lightning Punch' which could concivably shock someone holding the wrists of the character).
Sean: Sounds like your nightclub insurgent didn't take 'Restrainable' on his 0d6 HKA bite!
On a serious note, characters with an effective bite attack tend to have exaggerated/extended mandibles that would make it easier to restrain the bite, and therefore could be restrained. If they don't take 'Restrainable', then perhaps the reason is that they retain a very 'human' jaw structure which makes it easier for them to get under the restraining arm.
And for all: bigbywolfe is right. Don't let the rules get in the way of common and dramatic sense.