True. However, in both cases you were paying tax because you were working and then are not and without PHI are taking support from the state. Leaving aside how good they are and the Brown rip-off, pension schemes are tax exempt on the way in. It would seem reasonable for PHI, which is effectively doing a similar thing under different criteria, to be similarly catered for in tax terms.
On products I've seen, the benefit is RPI linked as long as the premium is increased on an RPI basis as well. Earnings increases above RPI are another issue of course.
As far as investment is concerned I was thinking of it more in terms of if one bought an insurance with premiums of X with no payout at the end, as opposed to one at X + Y with payout. In effect, you will have invested Y. That's out of net income. If you paid tax on the proceeds, it would be double taxation.