Basically, the devs deemed that regen would be too overpowered if we could enhance all of the regen of Integration and Instant Healing so they made it so that part was unenhanceable and the rest was enhanceable. This means that enhancements will only effect 100% of the 150% regen buff provided by Integration and 200% of the 800% buff provided by Instant Healing.
Since Issue 6 and the introduction of the wonderful ED, I don't think this is needed as much as we can no longer 6-slot.
Darn, those devs sure are naughty! 
In Character Builder it says,
Intergration -
Heal Rate : Heal( 197.2% ) ( Self ) - Changes depending on my enhancments
Heal Rate No Enhance : Heal( 50% ) ( Self ) - Does not change when enhanced.
Whats the Bold mean, is that an additional 50% that is not effected my enhancments? If so why, whats the point.
[Edit]
Just noticed another:
Instant healing -
Heal Rate : Heal( 394.4% ) ( Self ) - Changes depending on my enhancments
Heal Rate No Enhance : Heal( 600% ) ( Self ) - Does not change when enhanced.