I just think Triumph specifically de-tuned our bikes for the sake of reliability and their reputation (while still remaining comparitively competitive performance-wise in the cruiser market), which translates into sales.
The previous air-cooled Ducati SS900 pushed out 83 horses (I am comparing to the 865cc engine), so I am sure Triumph could achieve similar figures.
In the 4 years I have been checking out this site, not once have I heard of an engine failing (that is, without someone previously tampering with it), so I would say they have scored on the reliability front.
I would think that if Triumph were to significantly increase performance they would similarly probably have to upgrade on materials used, which in turn would increase costs etc.
That is, if they were to maintain the same current level of reliability.
The electrics/electronics is another story in which I do not have that much faith.
