I may be wrong but the purpose of PDL is to make it more fair for every military personnel. Take a Cpl and a LS for this example. One is in Valcartier and the other one in Victoria. Their monthly pay is the same, but the outcome at the end of the month is different. One can get a place for 450$ a month, the other one it's 950$, one can get car insurance for 225$ a year, the other one it's 850$. One can get a poutine for 3,50$ the other one it's 10$ (for the real stuff anyway).
Let me tell you, I' m an OS, incentive one with two kids and my wife dos not work yet. Without PDL it would be impossible for me to afford living in Victoria.
So, they don't give us PLD because they like us that much and they want us to be happy. It's a necessary measure if they want to have sailors around and people in other cities where it cost a lot to live.
They can't have different rules for every situation, so if you are reg force and live in one of those designated city, you get it. Does not matter if you refused a posting or you come from a wealthy family.
For the reserve part, I'm not well informed to comment too much but if you want PDL join the reg force!