I completely agree that one decoupler per power pin is a good rule of thumb.
I think it's always worth considering what such rules are trying to achieve, and to question or modify them where appropriate, though. In this case, a PIC is a low power, low frequency device, and I believe the extra inductance of (say) 5mm distance across a plane is insignificant.
It's worth mentioning that I design a lot of very, very small PCBs, where the cost of an extra cap isn't a problem but the size most definitely can be.
The only time I've had decoupling problems with a board was one in which the stack-up was wrong. In that case it was plane-to-plane capacitance that was lacking, and no discrete components would have helped. But that's a story for another day.